Wireless communication device and wireless communication method for providing opportunity of fair transmission to terminals

ABSTRACT

According to one embodiment, a wireless communication device includes a transmitter configured to transmit a first frame including information to specify a plurality of frequency components; and controlling circuitry configured to determine whether a second frame is received via each of the plurality of frequency components. The transmitter is configured to transmit a third frame including first information concerning a first value range which is used to determine whether to respond to the first frame, the first value range being dependent on a number of frequency components via which the second frame has been received.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.15/267,863, filed on Sep. 16, 2016, which is based upon and claims thebenefit of priority from Japanese Patent Application No. 2015-214878,filed on Oct. 30, 2015 and Japanese Patent Application No. 2016-180866,filed on Sep. 15, 2016; the entire contents of which are incorporatedherein by reference.

FIELD

Embodiments described herein relate to a wireless communication deviceand a wireless communication method.

BACKGROUND

Multi-user communication (multiplex communication) between a basestation and a plurality wireless communication terminals (hereinafter,referred to as terminals) is discussed. Uplink multi-user communicationis represented as UL-MU (UpLink Multi-User) communication, and downlinkmulti-user communication is represented as DL-MU (DownLink Multi-User)communication.

As the multi-user communication, frequency multiplexing communication isknown according to which different frequency components for eachwireless communication terminal (hereinafter referred to as terminal)are used as communication resources and transmissions to a plurality ofterminals and receptions from a plurality of terminals aresimultaneously performed. Here, Orthogonal Frequency Division MultipleAccess (OFDMA) scheme is considered where the frequency components aredefined as resource units each including one or a plurality ofsubcarriers, and the resource units each are used as a smallest unit ofthe communication resource, and transmissions to the plurality ofterminals or receptions from the plurality of terminals aresimultaneously performed. The simultaneous transmissions from the basestation to the plurality of terminals correspond to downlink OFDMA(DL-OFDMA) transmission and the simultaneous transmissions from theplurality of terminals to the base station correspond to uplink OFDMA(UL-OFDMA) transmission. The DL-OFDMA is an example of the DL-MU, andThe UL-OFDMA is an example of the UL-MU.

In a case of the UL-OFDMA, it may be considered that in order to matchtimings of uplink transmission, a trigger frame specifying terminalsthat are to be subjected to the UL-OFDMA and resource units allocated tothe terminals is transmitted from a base station. This method hasproblems that in a case such as where the specified terminal istransited to a sleep mode, or the specified terminal has no uplinktransmission request, the resource unit allocated to the specifiedterminal is not efficiently used and a usage efficiency of acommunication resource is decreased.

There is another method in which the trigger frame does not specify anyterminal, but specifies only resource units that are to be used. Themethod may include a case where a part of the resource units may bespecified with respect to a terminal, but remaining resource units arespecified with respect to no terminal. In any cases, the terminal towhich no resource unit is allocated, of the terminals receiving thetrigger frame, selects a resource unit randomly from the resource unitsspecified with respect to no terminal (also referred to as“STA-unspecified RU”) to use the selected resource unit. The triggerframe specifying the STA-unspecified RU may be called a trigger framefor random access.

Examples of the method selecting the resource unit randomly include thefollowing method. Every time the trigger frame for random access isreceived, a random number (backoff count) selected from a contentionwindow (CW) for random access is decremented by a value corresponding tothe number of STA-unspecified RUs. If the decremented backoff countbecomes below or 0, an access right with respect to the STA-unspecifiedRU is obtained, the resource unit is selected randomly fromSTA-unspecified RUs, and the frame is transmitted using the selectedresource unit. Note that the CW for random access is different from acontention window used for deciding a backoff time to carrier sense inCSMA/CA.

In the above method, if plural terminals simultaneously obtain theaccess right, these terminals may select the same STA-unspecified RU totransmit their frames. In this case, the frames transmitted from theseterminals collide at an access point, where the frames cannotsuccessfully be decoded. Each of these terminals does not receive anacknowledgement response from the access point, and thus, determinesthat the frame transmitted by the terminal is not successfully received.In this case, these terminals select a random number from the CW forrandom access which is newly set by way of receiving the next triggerframe for random access and perform the same process, but at this time,how the CW is selected again is not clear. Selecting the CW for randomaccess under the same condition as the terminal having succeeded in thetransmission (e.g., terminal not selecting the same resource unit asother terminals) may lack fairness. In addition, as for also theterminal from which the frame is successfully received at the accesspoint, how the CW is selected again is not clear. In this way, thismethod lacks a protocol for repeatedly using the trigger frame forrandom access.

Particularly, in a case where the trigger frame for random access isused to collect a UL-MU allocation request (uplink transmission request)from the terminals, the terminal having failed in the transmission fromwhich the request is not received by the access point is not selected asa terminal to be subjected to the UL-MU. On the other hand, the terminalhaving successfully transmitted the UL-MU allocation request may belikely to be selected in accordance with the request as a terminal to besubjected to the UL-MU (given an opportunity to transmit by way of theUL-MU). Therefore, selecting the CW for random access under the samecondition as the terminal having succeeded in the transmission may lackfairness.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a functional block diagram of a wireless communication deviceaccording to an embodiment of the invention;

FIG. 2 is a diagram illustrating resource unit allocation;

FIG. 3 is a diagram illustrating a form of a resource unit;

FIG. 4 is a diagram showing a wireless communication group including abase station and plural terminals;

FIG. 5 is a diagram showing an exemplary basic format of a MAC frame;

FIG. 6 is a diagram showing an exemplary format of an informationelement;

FIG. 7 is a diagram showing an example of a basic operational sequenceaccording to the embodiment of the invention;

FIG. 8 a diagram showing an exemplary format of a physical packet;

FIG. 9 is a diagram showing an exemplary format of a trigger frame(including a case of a trigger frame for random access);

FIG. 10 is a diagram showing an exemplary structure of an RU/AID field;

FIG. 11 is a supplementary illustration of the operational sequence inFIG. 7;

FIG. 12 is an illustration of a Multi-STA BA frame;

FIG. 13 is a diagram showing a schematic exemplary format of a physicalpacket used for DL-OFDMA transmission;

FIG. 14 is a diagram showing an example of an operational sequenceaccording to the embodiment of the invention;

FIG. 15 is a supplementary illustration of the operational sequence inFIG. 14;

FIG. 16 is a diagram schematically showing a state of update of a CWO(Contention Window for UL-OFDMA);

FIG. 17 is a diagram showing an exemplary operational sequence in a caseof transmitting a trigger frame instead of an acknowledgement responseframe;

FIG. 18 is a diagram schematically showing an operation according to amodification example 1 of CWO update;

FIG. 19 is a diagram schematically showing an operation according to amodification example 2 of the CWO update;

FIG. 20 a diagram showing an exemplary sequence of an operation of thebase station according to a modification example 4 of the CWO update;

FIG. 21 is a diagram showing an exemplary flowchart of an operation ofthe terminal according to the embodiment of the invention operation;

FIG. 22 is a diagram showing an exemplary flowchart of the operation ofthe base station according to the embodiment of the invention;

FIG. 23 is a functional block diagram of a base station or a terminal inaccordance with a second embodiment;

FIG. 24 is a diagram showing an exemplary entire configuration of theterminal or base station;

FIG. 25 is a diagram showing an exemplary hardware configuration of thewireless communication device installed at the terminal or base station;

FIG. 26 is a perspective view of the wireless communication terminalaccording to the embodiment of the invention;

FIG. 27 a diagram showing a memory card according to the embodiment ofthe invention; and

FIG. 28 is a diagram showing an example of frame exchange during acontention period.

DETAILED DESCRIPTION

According to one embodiment, a wireless communication device includes atransmitter configured to transmit a first frame including informationto specify a plurality of frequency components; and controllingcircuitry configured to determine whether a second frame is received viaeach of the plurality of frequency components. The transmitter isconfigured to transmit a third frame including first informationconcerning a first value range which is used to determine whether torespond to the first frame, the first value range being dependent on anumber of frequency components via which the second frame has beenreceived.

Hereinafter, embodiments of the present invention will be described withreference to the drawings. The entire contents of IEEE Std 802.11™-2012and IEEE Std 802.11ac™-2013, known as the wireless LAN specification andIEEE 802.11-15/0132r9 dated Sep. 22, 2015 which is SpecificationFramework Document directed to IEEE Std 802.11ax as a next generationwireless LAN standards are herein incorporated by reference in thepresent specification.

First Embodiment

A functional block diagram of a wireless communication device (or awireless device) according to the first embodiment of the presentinvention is illustrated in FIG. 1. This wireless communication devicecan be implemented in a wireless communication base station (hereinafterreferred to as a base station or an access point) or in a wirelesscommunication terminal (hereinafter referred to as a terminal) thatcommunicates with the base station. The base station is one mode of thewireless communication terminal (or the terminal) in that the basestation has the same or similar communication functions with those ofthe terminal with exception of the base station having a relay function.When a wireless communication terminal or a terminal is mentioned in thefollowing explanations, it may refer to a base station as long as theterminal and the base station should be particularly discriminated fromeach other.

A wireless communication system according to an embodiment includes abase station and plurality of terminals mounting therein a wirelesscommunication device shown in FIG. 1. In this system, OFDMA (OrthogonalFrequency Division Multiple Access) can be utilized for multi-usercommunication (multiplex communication). Uplink OFDMA is represented asUL-OFDMA. Downlink OFDMA is represented as DL-OFDMA. The systemaccording to the embodiment can implement at least the UL-OFDMA.Hereinafter, a description is given of the OFDMA.

In UL-OFDMA, resource units each including one or a plurality ofsubcarriers are assigned to terminals (the resource unit may also becalled subchannel, resource block, or frequency block), and receptionsfrom the plurality of terminals are performed simultaneously on resourceunit basis. The resource unit is a smallest unit of a resource forperforming communication.

FIG. 2 illustrates the resource units (RU #1, RU #2 . . . RU #K)arranged within a continuous frequency domain of one channel (which isdescribed here as the channel M). A plurality of subcarriers orthogonalto each other are arranged in the channel M, and a plurality of resourceunits including one or a plurality of continuous subcarriers are definedwithin the channel M. Although one or more subcarriers (guardsubcarriers) may be arranged between the resource units, presence of theguard subcarrier is not essential. A number for identification of thesubcarrier or the resource unit may be assigned to each carrier or eachresource unit in the channel. The bandwidth of one channel may be forexample, though not limited to these, 20 MHz, 40 MHz, 80 MHz, and 160MHz. One channel may be constituted by combining a plurality of channelsof 20 MHz. The number of subcarriers in the channel or the number ofresource units may vary in accordance with the bandwidth. Uplink OFDMAcommunication is realized by different resource units beingsimultaneously used by different terminals.

The bandwidths of the resource units (or the number of the subcarriers)may be same among the resource units, or the bandwidths (or the numberof the subcarriers) may vary depending on the individual resource units.An exemplary arrangement pattern of the resource units within onechannel is schematically illustrated in FIG. 3. The width direction onthe paper surface corresponds to the frequency domain direction. FIG.3(A) illustrates an example where a plurality of resource units (RU #1,RU #2 . . . RU #K) having the same bandwidth are arranged, and FIG. 3(B)illustrates another example where a plurality of resource units (RU#11-1, RU #11-2 . . . RU #11-L) having a larger bandwidth than that ofFIG. 3(A) are arranged. FIG. 3(C) illustrates a still another examplewhere resource units with three types of bandwidths are arranged. Theresource units (RU #12-1, RU #12-2) have the largest bandwidth, theresource unit RU #11-(L−1) has the bandwidth identical to that of FIG.3(B), and the resource units (RU #K−1, RU #K) have the bandwidthidentical to that of FIG. 3(A).

A specific example is illustrated. When the entire 20 MHz channel widthis used, 26 resource units (tones) may be specified for the 256subcarriers (tones) arranged within the 20 MHz channel width. In otherwords, nine resource units are specified in the 20 MHz channel width andthe bandwidth of the resource unit becomes smaller than the 2.5 MHzwidth. In the case of a 40 MHz channel width, 18 resource units arespecified therefor. In the case of an 80 MHz channel width, 37 resourceunits are specified. When this is extended, for example, in the case ofa 160 MHz channel width or an 80+80 MHz channel width, 74 resource unitsare specified. It will be appreciated that the width of the resourceunit is not limited to a particular value and resource units of varioussizes can be arranged.

Here, the number of resource units used by each terminal is not limitedto a particular value and one or a plurality of resource units may beused. When a terminal uses a plurality of resource units, a plurality ofresource units that are continuous in terms of frequency may be used, ora plurality of resource units that are located at positions away fromeach other may be allowed to be used. The resource unit #11-1 may beregarded as one example of a resource unit bonding the resource units #1and #2.

It is assumed here that subcarriers within one resource unit arecontinuous in the frequency domain. However, resource units may bedefined with use of a plurality of subcarriers that are arranged in anon-continuous manner. The channels used in uplink OFDMA communicationare not limited to one single channel but resource units may be reservedin another channel (see the channel N in FIG. 2, for example) arrangedat a location away in the frequency domain from the channel M as thecase of the channel M and thus the resource units in both the channel Mand the channel N may be used. The same or different modes of arrangingthe resource units may be used for the channel M and the channel N. Thebandwidth of the channel N is by way of example 20 MHz, 40 MHz, 80 MHz,160 MHz, etc. as described above but not limited to them. It is alsopossible to use three or more channels. It is considered here that thecombining of the channel M and the channel N may be regarded as onesingle channel.

It is assumed here that a terminal that implements OFDMA is successfulin carrying out reception and decoding (including demodulation, decodingof error correcting code, etc.) of a physical packet including a frameon a channel of at least the basic channel width (20 MHz channel widthif an IEEE 802.11a/b/g/n/ac standard-compliant terminal is regarded as alegacy terminal) at the legacy terminal that is to be backwardcompatible. With regard to the carrier sense, it is carried out in aunit of the basic channel width.

The carrier sense may encompass both physical carrier sense associatedwith busy/idle of CCA (Clear Channel Assessment) and Virtual CarrierSense based on medium reservation time indicated in the received frame.As in the case of the latter, a scheme for virtually determining that amedium is in the busy state, or the term during which the medium isvirtually regarded as being in the busy state is called NetworkAllocation Vector (NAV). Here, carrier sense information based on CCA orNAV carried out in a unit of a channel may be universally applied to allthe resource units within the channel. For example, resource unitsbelonging to the channel indicated as being in the idle state by thecarrier sense information are all in the idle state.

With regard to OFDMA, channel-based OFDMA is also applicable in additionto the above-described resource-unit-based OFDMA. OFDMA of this case mayin particular be called MU-MC (Multi-User Multi-Channel). In MU-MC, abase station assigns a plurality of channels (one channel width is, forexample, 20 MHz, etc.) to a plurality of terminals, and the plurality ofchannels are simultaneously used to carry out simultaneous transmissionsto the plurality of terminals or simultaneous receptions from theplurality of terminals. The OFDMA which will be described below meansthe resource-unit-based OFDMA: however, an embodiment of channel-basedOFDMA can also be implemented with appropriate replacement of terms andphrases in the following explanations such as reading the “resourceunit” as the “channel”.

In the following description, a terminal having the capability ofimplementing the OFDMA is referred to as an OFDMA-compliant terminal orthe like in some cases. A terminal not having the capability is referredto as a legacy terminal in some cases. In a case where the capability ofimplementing an OFDMA communication can be switched to be enabled ordisabled, a terminal of which the capability is enabled may beconsidered as the OFDMA-compliant terminal.

As illustrated in FIG. 1, a wireless communication device incorporatedin a terminal (which may be either a terminal of non-base station or thebase station) includes a upper layer processor 90, a MAC processor 10, aphysical (PHY) processor 50, a MAC/PHY manager 60, an analog processor70 (analog processors 1 to N), and an antenna 80 (antennas 1 to N),where N represents an integer equal to or larger than 1. In the figure,the N analog processors and the N antennas are connected in pairs witheach other, but the configuration is not limited to the illustrated one.For example, one analog processor and two or more antennas may beconnected to this analog processor in a shared manner.

The MAC processor 10, the MAC/PHY manager 60, and the PHY processor 50correspond to a mode of controller, controlling circuitry or basebandintegrated circuit that carries out processing associated withcommunications with other terminals (including the base station). Theanalog processor 70 corresponds, for example, to a wirelesscommunication unit or a radio frequency (RF) integrated circuit thattransmits and receives signals via the antenna 80. The integratedcircuit for wireless communication in accordance with this embodimentincludes at least the former of the baseband integrated circuit and theRF integrated circuit. The functions of the communication processingdevice or the baseband integrated circuit may be performed by software(programs) that runs on a processor such as a CPU or may be performed byhardware, or may be performed by both of the software and the hardware.The software may be stored in a storage medium such as a memory deviceincluding a ROM, a RAM, etc., a hard disk, or an SSD and read therefromto be executed. The memory device may be a volatile memory device suchas an SRAM or a DRAM, or a non-volatile memory device such as a NAND oran MRAM.

The upper layer processor 90 is configured to carry out processing forthe Medium Access Control (MAC) layer associated with the upper layer orlayers. The upper layer processor 90 is successful in exchanging signalswith the MAC processor 10. As the upper layer, TCP/IP, UDP/IP, and theapplication layer upper than these two protocols may be mentioned astypical examples but this embodiment is not limited to them. The upperlayer processor 90 may include a buffer for exchanging data between theMAC layer and the upper layer or layers. It may also be considered thatit may be connectable to a wired infrastructure via the upper layerprocessor 90. The buffer may be a memory device, an SSD drive, or a harddisk. When the buffer is a memory device, the memory device may be avolatile memory device such as an SRAM or a DRAM, or a non-volatilememory device such as a NAND or an MRAM.

The MAC processor 10 is configured to carry out processing for the MAClayer. As described above, the MAC processor 10 is successful inexchanging signals with the upper layer processor 90. Further, the MACprocessor 10 is successful in exchanging signals with the PHY processor50. The MAC processor 10 includes a MAC common processor 20, atransmission processor 30, and a reception processor 40.

The MAC common processor 20 is configured to carry out common processingfor transmission and reception in the MAC layer. The MAC commonprocessor 20 is connected to and exchanges signals with the upper layerprocessor 90, the transmission processor 30, the reception processor 40,and the MAC/PHY manager 60.

The transmission processor 30 and the reception processor 40 areconnected to each other. Also, the transmission processor 30 and thereception processor 40 are each connected to the MAC common processor 20and the PHY processor 50. The transmission processor 30 is configured tocarry out transmission processing in the MAC layer. The receptionprocessor 40 is configured to carry out reception processing in the MAClayer.

The PHY processor 50 is configured to carry out processing for aphysical layer (PHY layer). As described above, the PHY processor 50 issuccessful in exchanging signals with the MAC processor 10. The PHYprocessor 50 is connected via an analog processor 70 to an antenna 80.

The MAC/PHY manager 60 is connected to the upper layer processor 90, theMAC processor 10 (more specifically, the MAC common processor 20), andthe PHY processor 50. The MAC/PHY manager 60 is configured to manage MACoperation and PHY operation in the wireless communication device.

The analog processor 70 includes an analog-to-digital anddigital-to-analog (AD/DA) converter and a radio frequency (RF) circuit.The analog processor 70 is configured to convert a digital signal fromthe PHY processor 50 into an analog signal having a desired frequencyand transmit it from the antenna 80, or convert a high-frequency analogsignal received from the antenna 80 into a digital signal. It isconsidered here that although AD/DA conversion is carried out by theanalog processor 70, another configuration is also possible according towhich the PHY processor 50 has the AD/DA conversion function.

The wireless communication device in accordance with this embodiment hasits constituent element (i.e., incorporates) the antenna 80 in onesingle chip and thereby makes it possible to reduce the mounting area ofthe antenna 80. Further, in the wireless communication device inaccordance with this embodiment, as illustrated in FIG. 1, thetransmission processor 30 and the reception processor 40 shares the Nantennas 80. By virtue of sharing the N antennas 80 by the transmissionprocessor 30 and the reception processor 40, it is made possible toreduce the size of the wireless communication device of FIG. 1. It isconsidered here that the wireless communication device in accordancewith this embodiment may have a configuration different than the onedepicted by way of example in FIG. 1.

In reception of a signal from a wireless medium, the analog processor 70converts an analog signal received by the antenna 80 into a basebandsignal that can be processed by the PHY processor 50, and furtherconverts the baseband signal into a digital signal. The PHY processor 50is configured to receive a digital signal that is received from theanalog processor 70 and detect its reception level. The detectedreception level is compared with the carrier sense level (threshold).When the reception level is equal to or larger than the carrier senselevel, the PHY processor 50 outputs a signal indicative of the fact thatthe medium (CCA: Clear Channel Assessment) is in the busy state to theMAC processor 10 (the reception processor 40 to be more precise). Whenthe reception level is less than the carrier sense level, the PHYprocessor 50 outputs a signal indicative of the fact that the medium(CCA) is in the idle state to the MAC processor 10 (the receptionprocessor 40 to be more precise).

The PHY processor 50 is configured to carry out decoding processing forthe received signal (including demodulation and decoding of errorcorrecting code, etc.), processing of removing a physical header (PHYheader) including a preamble, or the like, and extracts a payload.According to IEEE 802.11 standard, this payload is called physical layerconvergence procedure (PLCP) service data unit (PSDU) on the PHY side.The PHY processor 50 delivers the extracted payload to the receptionprocessor 40, and the reception processor 40 handles it as a MAC frame.According to IEEE 802.11 standard, this MAC frame is called mediumaccess control (MAC) protocol data unit (MPDU). In addition, the PHYprocessor 50, when it started to receive the reception signal, notifiesthe fact of having started reception of the reception frame to thereception processor 40, and, when it completed the reception of thereception signal, notifies the fact of having completed the reception tothe reception processor 40. Also, the PHY processor 50, when thereception signal has been decoded successfully as the physical packet(PHY packet) (when it does not detect an error), notifies the completionof the reception of the reception signal and delivers a signalindicative of the fact that the medium is in the idle state to thereception processor 40. The PHY processor 50, when it detected an errorin the reception signal, notifies the fact that the error has beendetected with an appropriate error code in accordance with the errortype to the reception processor 40. Also, the PHY processor 50, at thetiming at which the medium has been determined to enter the idle state,notifies a signal indicative of the fact that the medium is in the idlestate to the reception processor 40.

The MAC common processor 20 performs intermediary processing fordelivery of transmission data from the upper layer processor 90 to thetransmission processor 30 and for delivery of reception data from thereception processor 40 to the upper layer processor 90. According toIEEE 802.11 standard, the data in this MAC data frame is called mediumaccess control (MAC) service data unit (MSDU). Also, the MAC commonprocessor 20 receives instructions from the MAC/PHY manager 60 and thenconverts the instruction into appropriate form of instructions for thetransmission processor 30 and the reception processor 40 and outputs theconverted instructions to these units.

The MAC/PHY manager 60 corresponds, for example, to station managemententity (SME) in IEEE 802.11 standard. In that case, the interfacebetween the MAC/PHY manager 60 and the MAC common processor 20corresponds to MAC subLayer management entity service access point (MLMESAP) in IEEE 802.11 standard, and the interface between the MAC/PHYmanager 60 and the PHY processor 50 corresponds to physical layermanagement entity service access point (PLME SAP) in IEEE 802.11wireless local area network (LAN).

It is considered here that although the MAC/PHY manager 60 in FIG. 1 isillustrated on the assumption that the functional unit for the MACmanagement and the functional unit for the PHY management are configuredto be integral with each other, these units may be separatelyimplemented.

The MAC/PHY manager 60 stores Management Information Base (MIB). The MIBstores various pieces of information such as the capability of thedevice itself and whether various functions are enabled or disabled. Forexample, information may be stored regarding whether or not the deviceitself supports OFDMA and, if the device itself supports OFDMA, whetheror not the function to implement OFDMA is enabled or disabled. A memorydevice for storing and managing the MIB may be incorporated in theMAC/PHY manager 60 or separately provided without being incorporatedinto the MAC/PHY manager 60. When the memory device for storing andmanaging the MIB is provided separately from the MAC/PHY manager 60, theMAC/PHY manager 60 can refer to the separately provided memory deviceand rewrite rewritable parameters within the memory device. The memorydevice may be a volatile memory device such as an SRAM or a DRAM, or anon-volatile memory device such as a NAND or an MRAM. Also, storagedevices such as a hard disk and an SSD may be used in place of thememory device. In the base station, these pieces of information of theother terminals that are not a base station can also be obtained bynotification from these terminals. In that case, the MAC/PHY manager 60is adapted to be successful in referring to and rewriting theinformation regarding the other terminals. Alternatively, the memorydevice for storing the information on the other terminals may be heldand managed separately from the MIB. In that case, either the MAC/PHYmanager 60 or the MAC common processor 20 is adapted to be successful inreferring to and rewriting the separate memory device. Also, the MAC/PHYmanager 60 of the base station may include a selection function for,when implementing OFDMA, selecting the terminals to which the resourceunits for OFDMA are assigned on the basis of various pieces ofinformation regarding terminals that are not a base station, or on thebasis of the requests from the terminals (i.e., selecting the terminalssubject to OFDMA of this time). Also, the MAC/PHY manager 60 or the MACprocessor 10 may manage the data (transmission) rate applied to the MACframe and the physical header aimed at transmission. Also, the MAC/PHYmanager 60 of the base station may define and manage a supported rateset which is a rate set supported by the base station. The supportedrate set may include a rate that should compulsorily supported by theterminal that is connected to the base station and an optional rate.

The MAC processor 10 is configured to handle three types of MAC frames,i.e., a data frame, a control frame, and a management frame, and carryout various processing procedures defined in the MAC layer. Here, thethree types of MAC frames are described.

The management frame is for use in management of communication link withanother terminal. As the management frame, for example, Beacon frame maybe mentioned. The Beacon frame notifies attribute and synchronizationinformation of a group to form a wireless communication group which is aBasic Service Set (BSS) in IEEE 802.11 standard. Also, a frame forauthentication or establishing the communication link may also bementioned. It is considered here that a state where a certain terminalcompleted exchange of information necessary for establishing a wirelesscommunication with another terminal is expressed here as (the statewhere) the communication link is established. As the exchange ofnecessary information, for example, notification of the functions thatthe device itself supports (for example, support of the OFDMA scheme andvarious capabilities which will be later described, etc.), andnegotiation regarding settings of the scheme may be mentioned. Themanagement frame is generated on the basis of the instruction receivedby the transmission processor 30 from the MAC/PHY manager 60 via the MACcommon processor 20.

With regard to the management frame, the transmission processor 30achieves notifying various pieces of information to other terminals bythe management frame. A terminal that is not a base station may notifythe type of the terminal itself to the base station by putting in themanagement frame information regarding such as whether it is anOFDMA-compliant terminal, an IEEE 802.11n-compliant terminal, or an IEEE802.11ac-compliant terminal. As for this management frame, for example,Association Request frame used in the association process which is oneof the procedures for authentication between the terminal and the basestation or Reassociation Request frame used in the reassociation processmay be mentioned. The base station may notify the information on whetheror not it supports UL-OFDMA communication to the terminal that is notthe base station by the management frame. As the management frame usedfor this, for example, Beacon frame and Probe Response frame may bementioned. The Probe Response frame is a response to the Probe Requestframe transmitted by the terminal that is not the base station. The basestation may have a function of grouping terminals which are connected toitself. The above-described notification means at the base station maynotify to each of the terminals a group ID by the management frame. Thegroup ID is a group identifier of the group to which the terminal itselfbelongs. As this management frame, for example, Group ID Managementframe may be mentioned. The group ID may be, for example, an identifierthat expands the concept of a group ID (six bits) defined for DL-MU-MIMOin IEEE Std 802.11ac-2013 such that it covers a case of OFDMA, or may bea group ID that is defined in accordance with a method different fromthis.

Here, association ID (AID) is described. The AID is an identifier of aterminal (terminal identifier) assigned by the base station to thisterminal in the association process for allowing the terminal to make aconnection to the base station and enabling data frame exchange in theBSS under the base station. The association process, specifically, is aprocess that becomes successful when an Association Request frame istransmitted from the terminal to the base station and an AssociationResponse frame is transmitted from the base station to the terminal andthe terminal Status Code field in the Association Response frame is 0which represents success. The communication capability of thetransmission terminal is included in both Association Request frame andAssociation Response frame, by virtue of which both parties thatreceived either of them grasp the communication capabilities of theircounterparts. When terminal Status Code field in the AssociationResponse frame is 0 representing success, the AID is extracted from theAID field (16 bits) in the same frame and it is used as the AID of thetransmission destination terminal. In other words, the AID is assignedfrom the base station to the terminal at this point, and the terminalenters a state where the AID is enabled. In a state where this basestation is connected to (have Association with) the terminal, the AID ofthe terminal is enabled. Meanwhile, when a Disassociation frame istransmitted from the base station to this terminal and this terminalreceives it, or when the Disassociation frame is transmitted from thisterminal to the base station, the AID of this terminal is disabled(null). It will be appreciated that the AID is null on a terminal thathas not had the association process with any base station. It can alsobe said that the state where the AID is null is a state where the AID isnot assigned.

The reception processor 40 has a receiver that receives various types ofinformation via the management frame from other terminals. As oneexample, the receiver of the base station may receive informationassociated with compatibility with OFDMA communication from any terminalas a non-base station. Also, it may receive information associated withan adaptable channel width (the maximum available channel width) if thisterminal is a legacy terminal (IEEE 802.11a/b/g/n/ac standard-compliantterminal and the like). The receiver of the terminal may receive fromthe base station information associated with compatibility as to whetheror not OFDMA is supported.

The examples of the information to be transmitted and received via themanagement frame as described above are merely examples and variousother types of information can be transmitted and received via themanagement frame between terminals (including the base station). Forexample, an OFDMA-compliant terminal may select either or both of aresource unit and a channel that the terminal itself wants to use in theOFDMA transmission from either or both of non-interference channels andnon-interference resources based on carrier sense. And informationregarding the resource unit, channel, or both of them that have beenselected may be notified to the base station. In this case, the basestation, on the basis of this information, may perform assignment of theresource units for the OFDMA communication for each of theOFDMA-compliant terminals. It is considered here that the channels usedin the OFDMA communication may be all of the channels that are availableas the wireless communication system or may be a subset (one or aplurality) of the channels.

The data frame is for use in transmission of data to another terminal ina state where the communication link is established with the otherterminal. For example, data is generated in the terminal by an operationof an application by a user, and the data is carried by the data frame.Specifically, the generated data is delivered from the upper layerprocessor 90, via the MAC common processor 20, and to the transmissionprocessor 30, the data is put into the frame body field by thetransmission processor 30, and a MAC header is added to the this framebody field, and thus the data frame is generated. In addition, aphysical header is added to the data frame by the PHY processor 50, thephysical packet is generated, and the physical packet is transmitted viathe analog processor 70 and the antenna 80. Also, when the physicalpacket is received by the PHY processor 50, the PHY processor 50performs the processing for the physical layer on the basis of thephysical header, and extracts the MAC frame (here, the data frame), anddelivers the data frame to the reception processor 40. When thereception processor 40 receives the data frame (recognizes that thereceived MAC frame is a data frame), the reception processor 40 extractsthe information in the frame body field as data, and delivers theextracted data via the MAC common processor 20 to the upper layerprocessor 90. As a result, operations occur on applications such aswriting, reproduction, and the like of the data.

The control frame is for use in control in transmission and reception(exchange) of the management frame and the data frame to/from (with) theother wireless communication device. As the control frame, for example,RTS (Request to Send) frame, CTS (Clear to Send) frame may be mentionedwhich are exchanged with the other wireless communication device to makea reservation of the wireless medium prior to starting exchange of themanagement frame and the data frame. Also, as another control frame,delivery confirmation response frame for confirmation of delivery of thereceived management frame and the data frame may be mentioned. Asexamples of the delivery confirmation response frame, ACK frame and BA(BlockACK) frame may be mentioned. Since the CTS frame is transmitted asa response to the RTS frame, it can be said that the CTS is a frame thatrepresents a delivery confirmation response. CF-End frame is also one ofthe control frames. The CF-End frame is a frame that announces thecompletion of the CFP (Contention Free Period) or the truncation of theTXOP after-mentioned, in other words, a frame permitting other wirelesscommunication devices to access the wireless medium. These controlframes are generated by the transmission processor 30. With regard tothe control frames (CTS frame, ACK frame, BA frame, etc.) transmitted asa response to the received MAC frame, the reception processor 40determines whether or not transmission of a response frame (controlframe) is necessary, and outputs information necessary for framegeneration (type of the control frame, information specified in the RA(Receiver Address) field, and the like) to the transmission processor 30along with the transmission instruction. The transmission processor 30generates an appropriate control frame on the basis of the informationnecessary for generation of the frame and the transmission instruction.

When a MAC frame is transmitted on the basis of CSMA/CA (Carrier SenseMultiple Access with Carrier Avoidance), the MAC processor 10 needs toacquire the access right (transmission right) on the wireless medium.The transmission processor 30, on the basis of carrier sense informationfrom the reception processor 40, measures the transmission timing. Thetransmission processor 30, in accordance with the transmission timing,gives the transmission instruction to the PHY processor 50, and furtherdelivers the MAC frame thereto. In addition to the transmissioninstruction, the transmission processor 30 may instruct a modulationmethod and a coding method to be used in the transmission. In additionto them, the transmission processor 30 may provide an instructionregarding the transmission power. When the MAC processor 10, afterhaving acquired the access right (transmission right), obtained theperiod of time during which the medium can be occupied (TransmissionOpportunity; TXOP), then the MAC processor 10 is allowed to continuouslyexchange the MAC frames with other wireless communication devicesalthough there is some limitation such as the QoS (Quality of Service)attribute. The TXOP is acquired, for example, when the wirelesscommunication device transmits a predetermined frame (for example, anRTS frame) on the basis of CSMA/CA (Carrier Sense Multiple Access withCarrier Avoidance) and correctively receives a response frame (forexample, a CTS frame) from another wireless communication device. Whenthis predetermined frame is received by the other wireless communicationdevice, the other wireless communication device transmits the aboveresponse frame after the elapse of the minimum frame interval (ShortInterFrame Space; SIFS). Also, as a method of acquiring the TXOP withoutusing the RTS frame, for example, cases may be mentioned where dataframe that requests transmission of the delivery confirmation responseframe is transmitted directly by the unicast (as will be describedlater, this frame may be a frame in the form of conjunct frames orconjunct payloads) or a management frame that requests transmission ofthe delivery confirmation response frame is transmitted, and deliveryconfirmation response frame (ACK frame, BlockACK frame or the like) inresponse thereto is correctly received. Alternatively, when a frame istransmitted that does not request, for the other wireless communicationdevice, transmission of the delivery confirmation response frame with aperiod equal to or longer than the time period needed to transmit thisframe specified in the Duration/ID field of this frame, then it may beinterpreted that with the transmission of this frame, TXOP of the perioddescribed in the Duration/ID field has been acquired.

The reception processor 40 is configured to manage the above-describedcarrier sense information. This carrier sense information includes bothPhysical Carrier Sense information regarding busy/idle states of themedium (CCA) input from the PHY processor 50 and Virtual Carrier Senseinformation on the basis of the medium reservation time described in thereceived frame. If either one of these carrier sense information piecesindicates the busy state, then the medium is regarded as being in thebusy state in which transmission is prohibited. It is considered herethat in IEEE 802.11 standard, the medium reservation time is describedin the Duration/ID field in the MAC header. The MAC processor 10, whenhaving received a MAC frame that is addressed to other wirelesscommunication devices (that is not addressed to the device itself),determines that the medium is virtually in the busy state from the endof the physical packet including this MAC frame over the mediumreservation time. A scheme of this type for virtually determining that amedium is in the busy state, or the term during which the medium isvirtually regarded as being in the busy state is called NetworkAllocation Vector (NAV). It can be said that the medium reservation timerepresents the length of time period during which suppression ofaccesses to the wireless medium is instructed, i.e., the length of timeperiod during which accesses to the wireless medium are deferred.

Here, the data frame may be a frame such that a plurality of MAC frames(i.e., MPDUs or sub-frames) are conjunct with each other or payloadportions of a plurality of MAC frames are conjunct with each other. Theformer data frame is called A (Aggregated)-MPDU and the latter dataframe is called A (Aggregated)-MSDU (MAC service data unit) in IEEE802.11 standard. In the case of the A-MPDU, a plurality of MPDUs areconjunct with each other within the PSDU. Also, as a MAC frame, inaddition to the data frame, the management frame and the control frameare also eligible for this conjunction. In the case of the A-MSDU, MPDUswhich are a plurality of data payloads are conjunct with each otherwithin the frame body of one MPDU. In both cases of the A-MPDU and theA-MSDU, partition information (length information, etc.) is stored inthe frame such that the conjunction of the MPDUs and combination ofMPDUs can be appropriately separated by the terminal on the receptionside. Both of the A-MPDU and the A-MSDU may be used in combination.Also, the A-MPDU may involve not a plurality of MAC frames (MPDUs orsub-frames) but one single MAC frame, and also in this case thepartition information is stored in the frame. Also, when an A-MPDU orthe like is received, responses to the plurality of MAC frames (i.e.,MPDUs or sub-frames) being conjunct are transmitted together. The BA(BlockACK) frame is used as the response in this case in place of theACK frame. In the following explanations and figures, the notation ofMPDU may be used, but it is assumed here that this notation includes thecases of the above-described A-MPDU and the A-MSDU.

According to IEEE 802.11 standard, several procedures are defined inmultiple stages to be taken for a terminal that is not the base stationto participate in a BSS (which is called Infrastructure BSS) configuredwith the base station amongst others and to perform exchange of dataframes within the BSS. For example, there is provided a procedure calledassociation, according to which an Association Request frame istransmitted from the terminal that is not the base station to the basestation to which the terminal requests the connection. The base station,after having transmitted an ACK frame for the association request frame,transmits an Association Response frame which is a response to theassociation request frame.

The terminal stores the capability of the terminal itself in theassociation request frame and transmits this association request frame,and thus can make notification of the capability of the terminal itselfto the base station. For example, the terminal may add, to theassociation request frame, the channel, the resource unit, or both ofthem that the terminal itself can support, and information foridentifying the standard supported by the terminal itself into theassociation request frame and transmit this association request frame.This information may be also set in the frame transmitted by theprocedure called reassociation (reassociation) to reconnect to anotherbase station. In this procedure of reassociation, a ReassociationRequest frame is transmitted to the other base station to whichreconnection is requested from the terminal. The other base station,after having transmitted the ACK frame in response to the reassociationrequest frame, transmits a reassociation response which is a response tothe reassociation request frame.

As the management frame, in addition to the association request frameand the reassociation request frame, a beacon frame, a probe responseframe, etc. may be used. The beacon frame is basically transmitted bythe base station, and is successful in storing parameter notifying thecapability of the base station itself along with the parametersindicating the attributes of the BSS. In view of this, as the parameternotifying the capability of the base station itself, the base stationmay be adapted to add the information on whether or not OFDMA issupported. Also, as the other parameter, information on the supportedrates of base station may be notified. The supported rates may includemandatory rates required to be supported by the terminals participatingin the BSS formed by the base station and an optional rate. The proberesponse frame is a frame transmitted from the terminal that transmitsthe beacon frame in response to a probe request frame received. Theprobe response frame is basically the one that notifies the same contentas that of the beacon frame, and the base station, when it uses theprobe response frame, is also successful in notifying the capability ofthe station itself to the terminal that transmitted the probe requestframe. By making this notification to the OFDMA-compliant terminal, anoperation may be performed according to which the terminal, for example,enables the function of the OFDMA communication of the terminal itself.

It is considered here that the terminal may notify the informationregarding the rates available on the device itself from among thesupported rates of the base station rate as the information fornotifying the capability of the device itself to the base station.Meanwhile, it is considered that with regard to the mandatory rates fromamong the supported rates, a terminal that is connected to the basestation has the capability of executing the mandatory rates.

It is considered here that if notification of some piece or pieces ofinformation among the pieces of information mentioned above leads todefinition of the content of another piece or other pieces ofinformation, then notification of the other piece or pieces ofinformation may be omitted. For example, suppose a case where a terminalis always an OFDMA-compliant terminal if a capability that is compliantwith a new standard or specifications is defined and as long as theterminal is compliant with that capability or specifications. In thiscase, as the above certain piece or pieces of information, presence ofthe capability to be compliant with the standard or specification isnotified, and as the other piece or pieces of information, notificationof the fact that the terminal is an OFDMA-compliant terminal does notneed to be explicitly performed.

FIG. 4 illustrates a wireless communication system in accordance withthis embodiment. This system includes the base station (AP: AccessPoint) 100 and a plurality of terminals (STA: STAtion) 1 to 8. The BSS(Basic Service Set) 1 is formed by the base station 100 and theterminals 1 to 8 operating under the base station 100. This system is awireless LAN system compliant with IEEE 802.11 standard using CSMA/CA(Carrier Sense Multiple Access with Carrier Avoidance). It is consideredhere that legacy terminals (IEEE 802.11a/b/g/n/ac standard-compliantterminals, etc.) other than the terminals (OFDMA terminals) inaccordance with this embodiment may exist within the BSS 1.

FIG. 5(A) illustrates the basic exemplary format of the MAC frame. Thedata frame, the management frame, and the control frame in accordancewith this embodiment are based on a frame format of this type. Thisframe format includes the fields of MAC header, Frame body, and FCS. TheMAC header includes, as illustrated in FIG. 5(B), the fields of FrameControl, Duration/ID, Address 1, Address 2, Address 3, Sequence Control,QoS Control, and HT (High Throughput) Control.

These fields do not need to always exist and there may be cases wheresome of these fields do not exist. For example, there may be a casewhere the Address 3 field does not exist. Also, there may be other caseswhere both or either one of the QoS Control field and the HT Controlfield does not exist. Also, there may be still other cases where theframe body field does not exist. Also, any field or fields that are notillustrated in FIG. 5 may exist. For example, an Address 4 field mayfurther exist. Also, an RU/AID field which will be described later mayexist in the MAC header or the frame body field. In a case of thetrigger frame described later, a common information field and a terminalinformation field may exist in a frame body field or a MAC header.

The field of Address 1 indicates Receiver Address (RA), the field ofAddress 2 indicates Transmitter Address (TA), and the field of Address 3indicates either BSSID (Basic Service Set IDentifier) which is theidentifier of the BSS, or TA, depending on the purpose of the frame. TheBSSID may be a wildcard BSSID whose bits are all set to 1 to cover allof the BSSIDs depending on the cases.

As described above, two fields of Type and Subtype (Subtype) or the likeare set in the Frame Control field. The rough classification as towhether it is the data frame, the management frame, or the control frameis made by the Type field, and more specific types, for example, finediscrimination among the roughly classified frames, for example, as towhether it is a BA frame, a BAR frame or CTS frame within the controlframe, or a beacon frame within the management frame is made by theSubtype field. The trigger frame which will be described later may alsobe discriminated by the combination of the Type and the Subtype. It islikely that the trigger frame is categorized as the control frame.

The Duration/ID field describes the medium reservation time, and it isdetermined that the medium is virtually in the busy state from the endof the physical packet including this MAC frame to the mediumreservation time when a MAC frame addressed to another terminal isreceived. The scheme of this type to virtually determine that the mediumis in the busy state, or the period during which the medium is virtuallyregarded as being in the busy state, is, as described above, called NAV(Network Allocation Vector). The QoS field is used to carry out QoScontrol to carry out transmission with the priorities of the framestaken into account. The HT Control field is a field introduced inIEEE802.11n.

In the management frame, an information element (Information element;IE) to which a unique Element ID (IDentifier) is assigned is set in theFrame Body field. One or a plurality of information elements subsequentto a specific field depending on the type of the management frame may beset in the frame body field. The information element has, as illustratedin FIG. 6, the fields of an Element ID field, a Length field, and anInformation field. The information element is discriminated by theElement ID. The Information field is adapted to store the content of theinformation to be notified, and the Length field is adapted to store thelength information of the information field.

Frame check sequence (FCS) information is set in the FCS field as achecksum code for use in error detection of the frame on the receptionside. As an example of the FCS information, CRC (Cyclic Redundancy Code)may be mentioned.

FIG. 7 shows an exemplary operational sequence of a base station (AP)101 and plural terminals including a terminal (STA) 1 to a terminal(STA) 8 according to the embodiment. Each of the terminals 1 to 8 is anOFDMA-compliant terminal. FIG. 7 shows a basic operational sequenceaccording to the embodiment and a description of an operation relatingto features of the embodiment is given later by means of anotherexemplary operational sequence (see FIG. 14).

In this exemplary operation sequence, as its premise, CSMA/CA-basedcommunications are individually carried out (single user communications)between the base station and all or part of the terminals 1 to 8. In thesingle user communications, communications are carried out between thebase station and the terminals, for example, on one channel with thebasic channel width (for example, 20 MHz). As one example of the singleuser communications, when data for uplink transmission is held by theterminal, the right to access the wireless medium is acquired inaccordance with CSMA/CA. As a result, the terminal carries out carriersense for the carrier sense time (standby time) during the DIFS/AIFS[AC]and a randomly defined back-off time, and when it has been determinedthat the medium (CCA) is in the idle state, the terminal acquires theright to access to transmit, for example, one frame. The terminaltransmits the data frame (more specifically, a physical packet includingthe data frame). When the base station has received this data framesuccessfully, then the base station returns an ACK frame (morespecifically, a physical packet including the ACK frame) which is adelivery confirmation response (acknowledgement) frame after the elapseof SIFS time after completion of reception of the data frame. Theterminal upon reception of the ACK frame determines that thetransmission of the data frame has been successful. It is consideredhere that the data frame to be transmitted to the base station may be anaggregation frame (A-MPDU, etc.), and the delivery confirmation responseframe by which the base station respond may be a BA frame (this alsoapplies to the following explanations). It is considered here that theDIFS/AIFS [AC] time refers to either the DIFS time or the AIFS [AC]time. When the terminal is not QoS-compliant, the DIFS/AIFS [AC] timerefers to the DIFS time. When the terminal is QoS-compliant, theDIFS/AIFS [AC] time refers to the AIFS [AC] time which is defined inaccordance with the access category (AC) (to be later described) of thedata to be transmitted. Note that the physical packet has a basicstructure in which the physical header is added to the MAC frame storedin a data field as shown in FIG. 8 described later.

The base station decides to start UL-OFDMA at any timing. This examplecontemplates a case where UL-OFDMA transmission is performed by the samechannel as that of the single user communication (one channel with thebasic channel width of 20 MHz). In other words, it is considered in thisexample that the UL-OFDMA transmission is performed using a plurality ofresource units defined within the channel with the basic channel widthof 20 MHz. Nevertheless, it is also possible to use other channel widthssuch as 40 MHz, 80 MHz, etc. to perform the UL-OFDMA transmission.

The base station, when deciding to start the UL-OFDMA, transmits thetrigger frame for UL-OFDMA, more specifically, the trigger frame forrandom access (further specifically, the physical packet including thetrigger frame for random access) 501.

The trigger frame for random access 501 defines that all or at least apart of the plural resource units offered for UL-OFDMA can be used byany terminal(s). The resource units are not assigned to specificterminals (the resource units are not limited to specific terminals).Such a resource unit may be called an “STA-unspecified RU”. However, thetrigger frame may define that resource units except STA-unspecified RUsout of the plural resource units offered for UL-OFDMA are allocated tospecific terminals. In this case, the resource units except theSTA-unspecified RUs are used by only the specific terminals. That is,the STA-unspecified RU is a resource unit which is permitted to beselected randomly and used (uplink transmission) among plural terminals.The trigger frame specifying the STA-unspecified RUs for at least a partof the resource units is called the trigger frame for random access. Thetrigger frame for random access is represented by “TF-R” in the figure.

When the trigger frame for random access 501 is transmitted, the basestation acquires the access right in advance based on the CSMA/CA. Thetrigger frame for random access 501 is transmitted at a channel havingthe basic channel width which is the same channel width as that of thesingle-user communication. The physical packet including the triggerframe for random access has the physical header added to the head of thetrigger frame for random access. The physical header includes, as anexample, an L-STF (Legacy-Short Training Field), an L-LTF (Legacy-LongTraining Field), and an L-SIG (Legacy Signal Field) which are defined byIEEE802.11 standard, as shown in FIG. 8. Each of the L-STF, the L-LTF,and the L-SIG is a field (legacy field) successful in being recognizedby a terminal corresponding to a legacy standard such as IEEE802.11a,for example, and information such as information for signal detection,information for frequency correction (channel estimation), andinformation on transmission rate is stored therein, respectively. Fieldsother than those described here (e.g., a field that cannot be recognizedby a legacy terminal but can be recognized by an OFDMA-compliantterminal) may be included. Note that the trigger frame for random access501 may be a frame successful in being received and decoded by a legacyterminal as well as an OFDMA-compliant terminal.

FIG. 9 is a diagram showing an exemplary format of the trigger frame(including a case of the trigger frame for random access). This has aformat of a general MAC frame as a base shown in FIG. 5 and includes theFrame Control field, the Duration/ID field, the Address 1 field, and theAddress 2 field, the common information field (Common Info.) field,plural terminal information (STA Information: STA Info) fields and theFCS field. The frame is specified to be the trigger frame by the Typeand Subtype fields in the Frame Control field. The Type is “control” asan example, and the Subtype may define a new value corresponding to thetrigger frame. However, the trigger frame can be defined with the Typebeing “management” or “data”. Note that, instead of defining a new valueas the Subtype, a reserved field of the MAC header can be used as afield notifying that a frame is the trigger frame. The Address 1 fieldmay be set to a broadcast address or a multicast address as an RA. TheAddress 2 field may be set to a MAC address of the base station (BSSID)as a TA. However, the Address 1 field or the Address 2 field, or both ofthem may be omitted in some cases. The common information field is setto notify information common to the plural terminals. For example,information specifying a format of the terminal information field,information specifying a length of the packet transmitted in response,information representing an intended purpose (or use application) of thetrigger frame, and information specifying a type of the frame to betransmitted in response to the trigger frame can be also set therein.Information on the number of the terminal information fields can be alsoset therein. Each of the plural terminal information fields setinformation which is to be notified to each of the plural terminals. Adetailed structure of the terminal information fields 1 to n is shown inFIG. 10. Each of the terminal information fields 1 to n includes an RUfield and an AID field.

Each of terminal information fields 1 to n includes a pair (set) of theRU field (RU_1 to RU_n) and the AID field (AID_1 to AID_n) as anexample. The RU field is set to an identifier of a resource unit thatcan be used. The AID field is set to an identifier (AID) of the terminalassigned to the resource unit or information indicating that usage ofthe resource unit is specified to no specific terminal (i.e.,STA-unspecified RU). In the embodiment, the information that the usageis specified to no specific terminal is represented by X as a value ofan unused AID. X is a value of the AID not assigned to any terminal, andhas a value defined beforehand in the system or by the standard, or avalue arbitrarily defined by the base station. The value of X may benotified by means of a management frame such as a beacon frame from thebase station to the terminals. The resource unit having X set therein isa resource unit which may be used by any terminal, that is, the resourceunit for random access or STA-unspecified RU.

Note that the terminal whose identifier is set in any of the AID fieldsmay be permitted to use or permitted not to use the resource unit forrandom access in addition to the resource unit specified to use. Theembodiment describes an aspect that if a terminal is allocated aspecific resource unit, the terminal does not use the resource unit forrandom access (STA-unspecified RU): however, the embodiment is notnecessarily limited thereto.

Note that the usage of the resource unit for random access may belimited to a plurality of specific terminals or a group having aspecific group ID. In the latter case, the AID field may be set to thegroup ID. In the former case, a plurality of AIDs may be set for one RUfield. Other method than those described here may be used.

Note that n (the number of sets of the RU field and the AID field) maybe fixed or variable. In the case of the variable value, a value of nmay be set in the common information field or a field notifying the endof the RU/AID field may be provided. The field notifying the end may bea field set to a special value which is not any of possible values ofthe sets of the identifier of the resource unit and the AID. Theterminal information field may include a field other than the RU fieldand AID field. For example, fields set information specifying atransmission power, a MCS and the like used by the terminal may beincluded.

Hereinafter, an example is shown in which a frame format having such aRU/AID field structure like this is used to make the plural terminalsselect the resource units randomly and transmit frames.

The trigger frame for random access (TF-R) 501 transmitted from the basestation is received by terminals 1 to 8. In this example, the triggerframe for random access 501 specifies four resource units (RU #1, RU #2,RU #3, and RU #4), and every resource unit has the AID set to X. Inother words, RU #1 to RU #4 are STA-unspecified RUs. However, thetrigger frame for random access 501 may specify more resource units, oran AID of a specific terminal may be specified for a part of theresource units.

Each of the terminals 1 to 8 decodes the trigger frame for random access501 to check whether or not the usage of any of four resource units RU#1 RU #2, RU #3, and RU #4 is specified to its own terminal, anddetermines that all the resource units are the resource unit for randomaccess (STA-unspecified RU) since here every resource unit has the AIDset to X. This determination is made by a MAC processor 10 (e.g., areception processor 30 or a MAC common processor 20), or a MAC/PHYmanager 60.

Each of terminals 1 to 8 holds a backoff count (UL-OFDMA Backoff (OBO)Count) selected randomly from a value range being not more than acontention window for UL-OFDMA (CWO) value. More specifically, thebackoff count selected from a value range from 0 to the CWO value isheld. The CWO corresponds to information concerning a value range. Inthis example, a size of the value range is equal to CWO (=CWO−0). Thelower limit of the value range may not be zero. The minimum value of theCWO is expressed as CWO min, and the maximum value of the CWO isexpressed as CWO max. The CWO is selected from a range from the CWO minto the CWO max. Here, 31 is selected as a predetermined initial value ofthe CWO. The CWO, the backoff count (OBO count), the CWO min, and theCWO max may be managed by the MAC processor 10, the MAC/PHY manager 60or the like, and these values may be stored in a memory accessible tothe MAC processor 10, the MAC/PHY manager 60 or the like.

Each of the terminals 1 to 8 subtracts, from its backoff count, thenumber of STA-unspecified RUs which is specified in the trigger framefor random access 501 to update the OBO. If the OBO after the updatereaches a predetermined value, the terminal acquires a right to selectthe STA-unspecified RU randomly (the right to select may be called aselection right below) and selects the STA-unspecified RU randomly.Thereby, the terminal acquires an access right to the selectedSTA-unspecified RU. In the embodiment, the predetermined value is 0. Ifa subtraction result is below 0, the OBO after the update is rounded upto 0. In this way, if the OBO count after the update reaches 0, theterminal acquires the selection right. In other words, when the triggerframe for random access is received, the OBO count is subtracted by 1(OBO count−1), and if the resulted value is equal to or less than avalue obtained by subtracting 1 from the number of STA-unspecified RUsin the trigger frame for random access (the number of STA-unspecifiedRUs−1), the selection right is acquired. In other words further, if theOBO count when the trigger frame for random access is received (OBOcount before the subtraction) is equal to or less than the number ofSTA-unspecified RUs in the trigger frame for random access, theselection right is acquired. The update of the OBO and the determinationon the selection right acquisition are made by the MAC processor 10(e.g., the MAC common processor 20 or the reception processor 40), orthe MAC/PHY manager 60.

Here, any terminals 1 to 8 are assumed to have an uplink transmissionrequest. The terminal having the transmission request holds the backoffcount selected from the range being not more than the CWO value asdescribed above. The first selection of the backoff count may be madewhen the transmission request is generated before receiving the triggerframe for random access 501, or may be triggered by the reception of thetrigger frame for random access 501. If another trigger frame for randomaccess is received before the trigger frame for random access 501 isreceived, the OBO count after the subtraction at that time may be usedas the OBO count (the OBO count before the subtraction this time) whenthe trigger frame for random access 501 is received.

FIG. 11 is a supplementary illustration for explaining the sequence inFIG. 7, and a lateral direction along a paper plane corresponds to timeand a longitudinal direction corresponds to frequency. The OBO counts ofthe terminals 1 to 8 (STAs 1 to 8) are

STA 1 OBO=10

STA 2 OBO=3

STA 3 OBO=5

STA 4 OBO=4

STA 5 OBO=1

STA 6 OBO=8

STA 7 OBO=8

STA 8 OBO=10

The number of STA-unspecified RUs is 4 in the trigger frame for randomaccess 501, and thus, the OBO counts after the update (subtraction)obtained by subtracting 4 from them are as below. The value below 0 isfixed to 0.

STA 1 OBO=10−4=6

STA 2 OBO=3−4=−1(−>0)

STA 3 OBO=5−4=1

STA 4 OBO=4−4=0

STA 5 OBO=1−4=−3(−>0)

STA 6 OBO=8−4=4

STA 7 OBO=8−4=4

STA 8 OBO=10−4=6

Terminals 2, 4, and 5 have the OBO count after the update reaching apredetermined value (=0), and thus, terminals 2, 4, and 5 acquire theselection right. Each of terminals 2, 4, and 5 selects the resource unitrandomly from RU #1 to RU #4 being STA-unspecified RUs which arespecified in the trigger frame for random access 501. Here, assume thatterminal 2 selects RU #4, terminal 4 selects RU #3, and terminal 5selects RU #1. The resource unit to select is one, but two or more maybe permitted to be selected. Other terminals than terminals 2, 4, and 5,which have the OBO count after the update larger than 0, cannot acquirethe selection right, and wait for the next transmitted trigger frame forrandom access. Note that the process of selecting the resource unit maybe made by the MAC processor 10 (e.g., the MAC common processor 20, thereception processor 40, or the transmission processor 30), or theMAC/PHY manager 60.

Terminals 2, 4, and 5 use RU #4, RU #3, and RU #1 to transmit frames512, 514, and 515, respectively, after elapse of a predetermined timeperiod (assuming T1) from completion of receiving the trigger frame forrandom access 501. The frames transmitted may be those of apredetermined kind or the frames arbitrarily decided by the terminals.Examples of the frames of a predetermined kind may include a UL-OFDMAallocation request frame (a frame notifying that there is a request ofdata transmission when a resource unit is allocated to its own terminalby a trigger frame). In this case, frames having a fixed length may beused to unify the lengths of frames transmitted by the terminals (morespecifically, the packet lengths of the physical packets including theframes). Parameter information such as the packet length, MCS or thelike for each terminal may be specified in the terminal informationfield, common information field, or the like in the trigger frame forrandom access 501 such that each terminal generates the frame inaccordance with the parameter information and transmits the frame (morespecifically, the physical packet including the frame). If the packetlength does not reach the specified value, padding data may be added toadjust the packet length. Note that since RU #2 is not selected by anyterminal, the transmission is not performed by use of RU #2. If otherresource unit than RU #1 to RU #4 exists and that resource unit isspecified for another terminal in the trigger frame for random access501, the terminal may transmit a frame using the specified resourceunit. In this case, the terminal and terminals 2, 4, and 5 are tosimultaneously perform the uplink transmission (UL-OFDMA transmission).Note that the frames transmitted from terminals 2, 4, and 5 may be anaggregation frame (A-MPDU), where frames such as the plural data frames(i.e., MPDUs or sub-frames) aggregated.

As for the time period T1, an IFS time [μs] defined beforehand may beused, as an example. The IFS time defined beforehand may be an SIFS time(=16 μs) that is a time interval of inter-frame defined by the MACprotocol specification for IEEE802.11 wireless LAN, or may be a timelarger or smaller than this. A value of the time period T1 may be storedin the common information field, a MAC header, or the like in thetrigger frame such that the terminal reads out this value to use.Besides, the time period T1 may be notified in advance in another waysuch as the beacon frame, other management frames, or the like.

The base station receives and decodes frames 515, 514, and 512transmitted from terminals 5, 4, and 2 in RU #1, RU #3 and RU #4 andsubjects the decoded frames to a FCS check (e.g., CRC check) todetermine whether or not the frames are successfully received. The basestation generates and transmits (downlink response) an acknowledgementresponse frame 502 depending on check results (success or failure of thereception) of the frames. Here, single acknowledgement response frame502 is transmitted which represents acknowledgements for all theterminals 2, 4, and 5. A format of the acknowledgement response framelike this may be newly defined or the Multi-STA BA frame obtained bydiverting the BA (Block Ack) frame thereto may be used. Here, theMulti-STA BA frame is transmitted.

A description is given of the Multi-STA BA frame here. The Multi-STA BAframe is obtained by diverting the Block Ack frame (BA frame) thereto inorder to make the acknowledgement to plural terminals by one frame. Aframe type may be “Control” similarly to the ordinary BA frame, and aframe subtype may be “BlockAck”. FIG. 12(A) shows an exemplary frameformat in the case of reusing the Multi-STA BA frame. FIG. 12(B) showsan exemplary frame format of a BA Control field of the BA frame, andFIG. 12(C) shows an exemplary frame format of a BA Information field ofthe BA frame. In the case of reusing the BA frame, an indication may bein the BA Control field that the BA frame format is that extended fornotifying the acknowledgement response regarding the plural wirelessterminals. For example, in IEEE802.11 standard, a case where a Multi-TIDsubfield is 1 and a Compressed Bitmap subfield is 0 is reserved. Thismay be used in order to indicate that the BA frame format is extendedfor notifying the acknowledgement response regarding to plural wirelessterminals. Alternatively, an area of bits B3-B8 is a reserved subfieldin FIG. 12(B), but all or a part of this area may be defined in order toindicate that the BA frame format is that extended for notifying theacknowledgement response regarding to plural wireless terminals.Alternatively, the notification as described here may not be necessarilymade explicitly.

The RA field of the Multi-STA BA frame may be set to a broadcast addressor a multicast address as an example. A Multi-User subfield in the BAControl field may be set to the number of the users (number of theterminals) to be reported by means of the BA Information field. In theBA Information field, there are arranged for each user (terminal), anAssociation ID subfield, a Block Ack Starting Sequence Control subfield,and a Block Ack Bitmap subfield.

The Association ID subfield is set to the AID for identifying the user.More specifically, as an example, a part of a Per TID Info field is usedas the subfield for the Association ID as shown in FIG. 12(C).Currently, 12 bits (from B0 to B11) are a reserved area. The first 11bits (B0-B10) of these are used as the subfield for the Association ID.The Block Ack Starting Sequence Control subfield and the Block AckBitmap subfield may be omitted if the frame transmitted by the terminalis a single data frame (that is, it is not an aggregation frame). If theframe transmitted by the terminal is an aggregation frame, the Block AckStarting Sequence Control subfield has stored therein a sequence numberof the first MSDU (medium access control (MAC) service data unit) in theacknowledgement response shown by the Block Ack frame. In the Block AckBitmap subfield, a bitmap (Block Ack Bitmap) constituted by bits eachshowing reception success or failure for the sequence numbers subsequentto the Block Ack Starting Sequence number is set.

The terminal receiving the Multi-STA BA frame 502 confirms the Type andSubtype of the Frame Control field. If the terminal detects that theseare “Control” and “BlockAck”, then the terminal confirms the RA field.Since the value of the RA field is the broadcast address or the like,the terminal identifies, from the Block Ack Bitmap field, theinformation on the acknowledgement responses (success or failure) withrespect to the MPDUs (sub-frames) in the frame (here, assumed that theframe is an aggregation frame) transmitted by its own terminal todetermine transmission success or failure of each sub-frame. Forexample, the terminal identifies the TID Info subfield storing its AIDfrom within the BA Information field, identifies the value (startingsequence number) set in the Block Ack Starting Sequence Control subfieldsubsequent to the identified TID Info subfield, and identifies from theBlock Ack Bitmap the transmission success or failure of each of thesequence numbers subsequent to the starting sequence number. A bitlength of the AID may be shorter than a length of the TID Info subfield,and the AID may be stored in a part of the area of the TID Info subfield(e.g., the first 11 bits (B0-B10) of 2 octets (16 bits)), for example.

The case where the plural terminals each transmits not the aggregationframe but a single frame by way of the UL-OFDMA (this case is assumed inthe sequence in FIG. 7) may be made as below, for example. As shown inFIG. 12(C), one bit in the TID Info subfield of each BA Informationfield (e.g., the 12th bit (B11, if the first bit is B0) from the head of2 octets (16 bits)) is used as a bit indicating “ACK” or “BA” (ACK/BAbit) and the bit is set to a value indicating “ACK”. If the valueindicating “ACK” is set, the Block Ack Starting Sequence Controlsubfield and the Block Ack Bitmap subfield are omitted.

This allows notification of “ACK” for the plural terminals by means ofone BA frame. The terminal of which the check result is failure is notnecessary to be notified of the ACK, and thus, the notificationregarding the terminal may not be made in the Multi-STA BA frame. Theterminal on the receiving side does not receive the ACK for its ownterminal and can determine that it has failed in the transmission. Inthis way, even if the plural terminals transmit either the aggregationframe or the single frame, the acknowledgement can be made with respectto the plural terminals by means of the single acknowledgement responseframe obtained by diverting the BA frame thereto.

The access point, in the case of transmitting the Multi-STA BA frame502, may transmit the Multi-STA BA frame 502 at the same frequency bandas the trigger frame for random access 501 or the UL-OFDMA, or at abandwidth of the basic channel width of 20 MHz, for example.

As other method than of transmitting the Multi-STA BA frame, theacknowledgement response frame (ACK frame, BA frame, or the like) may beindividually transmitted for each terminal. At this time, the DL-OFDMAmay be used to simultaneously transmit the acknowledgement responseframes to the plural terminals.

FIG. 13 shows an exemplary structure of the physical packet in the casewhere the acknowledgement response frames is transmitted to the pluralterminals by way of the DL-OFDMA. The L-STF, L-LTF, and L-SIG fieldsare, as an example, transmitted at a channel width of 20 MHz and set tothe same value (same symbol) for all acknowledgement response frameseach terminal headed. The SIG 1 field sets common information for aplurality of terminals and specifies, for example, the resource unit tobe used for the reception by each terminal. For example, informationassociating the terminal identifier with the resource unit number(identifier) is set. The terminal identifier may be the Association ID(AID), a part of the AID (Partial AID), or other identifier such as theMAC address. The SIG 1 field is also transmitted at a channel width of20 MHz, as an example. Any of the terminals can decode the SIG 1 field.The SIG 2 field is individually set for each resource unit andinformation on the MCS and the like which is required for decoding thecorresponding data field, as an example, may be set therein. Therefore,each terminal receiving the signal from the access point can detect, bydecoding the SIG 1 field, the proper resource unit to be decoded by itsown terminal. Each terminal decodes the resource unit specified to itsown terminal to receive the acknowledgement response frame. Note thatthe exemplary format in FIG. 13 is an example, and one or more otherfields may be arranged before or after the SIG 2 field, or before orafter the SIG 1 field. The other fields may have a bandwidth of 20 MHzor a resource unit width. All or a part of the other fields may beconstituted by known symbols similar to the L-STF and L-LTF.

As a method other than that of transmitting the acknowledgement responseframes to the plural terminals by way of the DL-OFDMA, theacknowledgement response frames may be transmitted to the pluralterminals by way of the downlink MU-MIMO. The DL-MU-MIMO uses atechnology called beam forming to form beams spatially orthogonal toeach other the plural terminals for performing the transmission. TheDL-MU-MIMO may be performed in accordance with IEEE802.11ac standardbased on which it is defined.

The base station, after transmitting the Multi-STA BA frame 502,transmits a trigger frame for random access 503 at a predeterminedtiming or an arbitrary timing. The trigger frame for random access 503has a structure similar to the trigger frame for random access 501, andspecifies RU #1 to RU #4 as the STA-unspecified RUs. Any transmissionmay be performed between the transmission of the Multi-STA BA frame 502and the transmission of the trigger frame for random access 503. Forexample, the ordinary trigger frame (trigger frame not specifying theSTA-unspecified RU) may be used to perform the UL-OFDMA communication.

Terminals 1 to 8 hold the OBO count (backoff count) updated when thetrigger frame for random access 501 was received last time. However,terminals 2, 4, and 5 which performed the transmission in reply to thetrigger frame for random access 501 (random access) again re-obtain theOBO count from the range from 0 to the CWO. Here, assume the CWO valueis the same value 31 as that used at last time. Then, assume thatterminals 2, 4, and 5 select, from [0, 31], 23, 7, and 18, respectively.Therefore, the OBO counts of terminals 1 to 8 (STAs 1 to 8) are asbelow.

STA 1 OBO=6

STA 2 OBO=23

STA 3 OBO=1

STA 4 OBO=7

STA 5 OBO=18

STA 6 OBO=4

STA 7 OBO=4

STA 8 OBO=6

The number of STA-unspecified RUs is 4 in the trigger frame for randomaccess 503, and thus, the OBO counts after the update (subtraction)obtained by subtracting 4 from the OBO counts of the terminals are asbelow. The value below 0 is fixed to 0.

STA 1 OBO=6−4=2

STA 2 OBO=23−4=19

STA 3 OBO=1−4=−3(−>0)

STA 4 OBO=7−4=3

STA 5 OBO=18−4=14

STA 6 OBO=4−4=0

STA 7 OBO=4−4=0

STA 8 OBO=6−4=2

Terminals 3, 6, and 7 have the OBO count after the update reaching apredetermined value (=0), and thus, terminals 3, 6, and 7 acquires theselection right. Each of the terminals 3, 6, and 7 selects the resourceunit randomly from RU #1 to RU #4 being STA-unspecified RUs which arespecified in the trigger frame for random access 503. Here, assume thatterminal 3 selects RU #2, terminal 6 selects RU #4, and terminal 7selects RU #1. The resource unit to select is one, but two or more maybe permitted to be selected. Other terminals than terminals 3, 6, and 7,which have the OBO count after the update larger than 0, cannot acquirethe selection right, and wait for the next transmitted trigger frame forrandom access.

Terminals 3, 6, and 7 use RU #2, RU #4, and RU #1 to transmit frames523, 526, and 527, respectively, after elapse of a predetermined timeperiod from completion of receiving the trigger frame for random access503. The frames transmitted may be those of a predetermined kind or theframes arbitrarily decided by the terminals. Note that since RU #3 isnot selected by any terminal, the transmission is not performed in RU#3. If other resource unit than RU #1 to RU #4 may be specified foranother terminal in the trigger frame for random access 503, and in thatcase, the terminal may transmit a frame by use of the specified resourceunit. In this case, the terminal and terminals 3, 6, and 7 are tosimultaneously perform the uplink transmission (UL-OFDMA transmission).Note that the frames transmitted from terminals 3, 6, and 7 may be anaggregation frame (A-MPDU), where frames such a plural data frames(i.e., MPDUs or sub-frames) being aggregated.

The base station receives and decodes frames 527, 523, and 526transmitted from terminals 7, 3, and 6 by use of RU #1, RU #2 and RU #4and subjects the decoded frames to the FCS check (e.g., CRC check) todetermine whether or not the frames are successfully received. The basestation generates and transmits (downlink response) an acknowledgementresponse frame depending on check results (success or failure of thereception) of the frames. Similarly to the above description, here, aMulti-STA BA frame 504 is transmitted as the single acknowledgementresponse frame which represents acknowledgements for all the terminals3, 6, and 7. The operation of the terminal having received the Multi-STABA frame 504 is the same as in the case of the Multi-STA BA frame 502.

Based on the description above, a description is given of a sequence ofthe operation relating to features of the embodiment. FIG. 14 shows anexample of the sequence. Elements the same as or corresponding to thosein FIG. 7 are designated by the same reference signs. FIG. 15 is asupplementary illustration for explaining the sequence in FIG. 14. Inthe exemplary sequence in FIG. 7 as described previously, when each ofthe plural terminals acquiring the selection right to theSTA-unspecified RU selects the resource unit randomly, the resourceunits selected by the terminals are different. For this reason, theframes transmitted from the terminals are successfully received by thebase station. In contrast to this, in the exemplary sequence in FIG. 14,assume that the terminals select the same resource unit, and the basestation cannot successfully receive the frames transmitted from theplural terminals. In such a case, the embodiment has a feature that theCWO value is adjusted such that a priority for acquiring the selectionright for the terminal having failed in the transmission is heightened(in FIG. 7 described previously, the CWO value was fixed to 31). As anexample, in this sequence, the CWO value is lowered than the last timeCWO value for the terminal having failed in the transmission. Thecontrol like this keeps the fairness between the terminals. Hereinafter,the sequence in FIG. 14 is described in detail. A description is mainlygiven of differences from that for FIG. 7 and the descriptionoverlapping that for FIG. 7 is omitted.

The base station, when deciding to start the UL-OFDMA, transmits thetrigger frame for random access (TF-R) 501. The trigger frame for randomaccess 501 specifies four resource units (RU #1, RU #2, RU #3, and RU#4), and every resource unit has the AID set to X in the AID field asthe STA-unspecified RUs.

Each of the terminals 1 to 8 decodes the trigger frame for random access501 and determines that none of four resource units RU #1 RU #2, RU #3,and RU #4 is specified to its own device and all the resource units arethe resource unit for random access since here every resource unit hasthe AID set to X.

Each of the terminals 1 to 8 holds the backoff count (OBO count)selected from a value range from 0 to the CWO value. The CWO is selectedfrom a range between the CWO min and the CWO max. Here, assume thatevery terminal selects the initial value CWOinit (=31). Each ofterminals 1 to 8 subtracts the number of STA-unspecified RUs in thetrigger frame for random access 501 from its backoff count to update itsOBO count. If the OBO count after the update reaches a predeterminedvalue (here, 0), the relevant terminal acquires the selection right tothe STA-unspecified RU.

Here, the OBO counts of terminals 1 to 8 (STAs 1 to 8) are

STA 1 OBO=10

STA 2 OBO=3

STA 3 OBO=5

STA 4 OBO=4

STA 5 OBO=1

STA 6 OBO=8

STA 7 OBO=2

STA 8 OBO=10

The number of STA-unspecified RUs is 4 in the trigger frame for randomaccess 501, and thus, the OBO counts after the update obtained bysubtracting 4 from them are as below. The value below 0 is fixed to 0.

STA 1 OBO=6−4=2

STA 2 OBO=23−4=19

STA 3 OBO=1−4=−3(−>0)

STA 4 OBO=7−4=3

STA 5 OBO=18−4=14

STA 6 OBO=4−4=0

STA 7 OBO=4−4=0

STA 8 OBO=6−4=2

Terminals 2, 4, 5 and 7 have the OBO count after the update reaching apredetermined value (0), and thus, terminals 2, 4, 5 and 7 acquire theselection right. Each of terminals 2, 4, 5 and 7 selects the resourceunit randomly from RU #1 to RU #4 being STA-unspecified RUs which arespecified in the trigger frame for random access 501. Here, assume thatterminal 2 selects RU #4, terminals 4 and 7 select RU #3, and terminal 5selects RU #1. Terminal 4 and terminal 7 select the same resource unit.Other terminals than terminals 2, 4, 5 and 7, which have the OBO countafter the update larger than 0, cannot acquire the selection right, andwait for the next transmitted trigger frame for random access.

Terminals 2, 4, 5 and 7 use RU #4, RU #3, RU #1 and RU #3 to transmitframes 512, 514, 515 and 517, respectively, after elapse of apredetermined time period from completion of receiving the trigger framefor random access 501. Terminal 4 and terminal 7 transmit the frames byuse of the same resource unit (see a shaded area in FIG. 15).

The base station performs the process to receive and decode frame 515transmitted from terminal 5 by use of RU #1, frames 514 and 517transmitted from terminals 4 and 7 by use of RU #3, and the frame 512transmitted from terminal 2 by use of RU #4, and subjects the decodedframes to the FCS check (e.g., CRC check) to determine whether or notthe frames are successfully received. Assume that frame 515 fromterminal 5 transmitted via RU #1 and frame 512 from terminal 2transmitted via RU #4 are successfully received, and frames 514 and 517transmitted via RU #3 from terminals 4 and 7 are failed to be received.

The base station generates and transmits, depending on check results(success or failure of the reception) of the frames, a Multi-STA BAframe 507 as the acknowledgement response frame including an indicationthat frames 512 and 515 transmitted from terminals 2 and 5 aresuccessfully received. Since frames 514 and 517 transmitted fromterminals 4 and 7 are failed to be received, the acknowledgement withrespect to each of terminals 4 and 7 is not included in the Multi-STA BAframe 507. Note that in a case where the aggregation frame including theplural data frames (i.e., MPDUs or sub-frames) is transmitted from eachof terminals 4 and 7, if all of the aggregated data frames (i.e., MPDUsor sub-frames) are failed to be received, the acknowledgement withrespect to each of terminals 4 and 7 may not be included in theMulti-STA BA frame 507. On the other hand, if a part of the aggregateddata frames (i.e., MPDUs or sub-frames) are successfully received, theacknowledgement concerning the data frames a part of which issuccessfully received may be included through the Block Ack StartingSequence Control subfield and the Block Ack Bitmap subfield.

Of the terminals receiving the Multi-STA BA frame 507, terminals 2, 4, 5and 7 confirm whether or not the acknowledgement with respect to each offrames 512, 514, 515 and 517 transmitted from them is included in theMulti-STA BA frame 507. Terminals 2 and 5 detect that theacknowledgement for each of the frames 512 and 515 transmitted from themis included, but terminals 4 and 7 cannot confirm the acknowledgementfor each of the frames 514 and 517 transmitted from them and determinethat they failed in the transmission. Here, having failed in thetransmission includes, not only a case (this case) where the basestation cannot successfully receive frames transmitted from the pluralterminals by use of the same resource unit, but also a case where thebase station fails to receive a frame transmitted from a single terminalin a certain resource unit, which is caused by a bad radiowaveenvironment. If the downlink response frame such as the Multi-STA BAframe is not received within a certain time period (SIFS time or thelike) from the completion of transmitting frames 512, 514, 515 and 517,the failure in transmission may be determined. Note that if the terminaltransmits the aggregation frame in which the plural data frames areaggregated and a part of the data frames are transmitted successfully,the terminal may determine the success in the transmission (randomaccess), as an example, and if all the data frames are failed to betransmitted, the terminal may determine the failure in the transmission(random access).

The base station, after transmitting the Multi-STA BA frame 507,transmits the trigger frame for random access 503 at a predeterminedtiming or an arbitrary timing. The trigger frame for random access 503has a structure similar to the trigger frame for random access 501, andspecifies RU #1 to RU #4 as the STA-unspecified RU. Note that anytransmission may be performed between after the transmission of theMulti-STA BA frame 507 and before the transmission of the trigger framefor random access 503. For example, the ordinary trigger frame (atrigger frame specifying a terminal for each resource unit) may betransmitted by the base station such that the terminals use respectivespecified resource unit to perform communication in uplink transmission(UL-OFDMA).

Terminals 1 to 8 hold the OBO count (backoff count) updated when thetrigger frame for random access 501 was received last time. However,terminals 2, 4, 5 and 7 which performed the random access to the triggerframe for random access 501 again select the OBO count from the rangefrom 0 to the CWO. However, terminals 2 and 5 succeeded in thetransmission, and terminals 4 and 7 failed in the transmission.Therefore, the embodiment has a feature that the CWO is selected asbelow.

Terminals 4 and 7 having failed in the transmission select the CWOsmaller than the last one (CWO=31) from a range between the CWO min andthe CWO max. The CWO is gradually decreased until the CWO min for everytransmission failure. In the case of success in the transmission, theCWO is returned to the initial value CWOinit (e.g., 31).

As an example, assume that CWO min=1 and CWO max=31, and the initialvalue CWOinit is 31 as the CWO max. Every time the transmission hasfailed, the CWO is gradually decreased from 31 to 1. Beginning from 31,a constant value may be cumulatively subtracted every transmissionfailure, or as the number of the failure increases, a larger value maybe cumulatively subtracted. As an example of the latter, it may be that1 is subtracted caused by the first failure, 2 is subtracted caused bythe second failure, and 3 is subtracted caused by the third failure. Inthis case, if the CWO at the start is 31, the CWO after the firstfailure is 30 (=31−1), after the second failure, 28 (=30−2), and afterthe third failure, 25 (=28−3) - - - . The adjustment amount (changingamount) by which the CWO is to be adjusted (changed) may be notifiedfrom the base station to each terminal as information concerning theCWO. The method for notifying the adjustment amount may be same as orsimilar to other notification methods as described later.

As another method, an exponent part P may be used to define acalculation formula of the CWO as 2{circumflex over ( )}P−1, forexample, and decrease the value of P every transmission failure. As anexample, in the case of the CWO max, if P=5, CWO max=2{circumflex over( )}5−1=31. In the case of CWO min=1, if P=1, CWO min=2{circumflex over( )}1−1=1. Assume, at the beginning, the CWO coincides with the CWO max.In this case, every transmission failure, the CWO is updated as below.

At the beginning 31 (=2{circumflex over ( )}5−1)

-   -   -<in failure>→15 (=2{circumflex over ( )}4−1)        -   -<in failure>→7 (=2{circumflex over ( )}3−1)            -   -<in failure>→3 (=2{circumflex over ( )}2−1)                -   -<in failure>→1 (=2{circumflex over ( )}1−1)

This state is schematically shown in FIG. 16. In the case of the successin the transmission, the CWO is returned to CWO max=31. The value of Pmay be notified from the base station to each terminal as informationconcerning the CWO. The method for notifying the value of P may be sameas or similar to other notification methods as described later. Thevalue of P is one example of the above adjustment amount.

In the case of the latter method, in this sequence, terminals 4 and 7each has the CWO of 15 (=2{circumflex over ( )}4−1), for example, afterthe first transmission failure. Terminals 2 and 5, which have succeededin the transmission, use the CWO that is still the initial CWOinit (=CWOmax) of 31 (=2{circumflex over ( )}5−1).

Terminals 4 and 7 select the OBO count (backoff count) from [0, 15]randomly, and assume that terminal 4 selects 7 and terminal 7 selects 4.Terminals 2 and 5 select the OBO count (backoff count) from [0, 31]randomly, and assume that terminal 2 selects 23 and terminal 5 selects18. Other terminals than these use the OBO count currently held by themas it is.

Therefore, the OBO counts of terminals 1 to 8 (STAs 1 to 8) are as below(as a result, it happens that the OBO counts of the terminals are thesame as in the case of the exemplary sequence in FIG. 7).

STA 1 OBO=6

STA 2 OBO=23

STA 3 OBO=1

STA 4 OBO=7

STA 5 OBO=18

STA 6 OBO=4

STA 7 OBO=4

STA 8 OBO=6

The number of STA-unspecified RUs is 4 in the trigger frame for randomaccess 503, and thus, the OBO counts after the update obtained bysubtracting 4 from the OBO counts of the terminals are as below. Thevalue below 0 is fixed to 0 (as a result, it happens that the OBO countsof the terminals are the same as in the case of the exemplary sequencein FIG. 7).

STA 1 OBO=6−4=2

STA 2 OBO=23−4=19

STA 3 OBO=1−4=−3(−>0)

STA 4 OBO=7−4=3

STA 5 OBO=18−4=14

STA 6 OBO=4−4=0

STA 7 OBO=4−4=0

STA 8 OBO=6−4=2

Terminals 3, 6, and 7 have the OBO count after the update reaching apredetermined value (0), and thus, terminals 3, 6, and 7 acquire theselection right. Terminals 3, 6, and 7 each selects the resource unitrandomly from RU #1 to RU #4 being STA-unspecified RUs which arespecified in the trigger frame for random access 503. Here, assume thatterminal 3 selects RU #2, terminal 6 selects RU #4, and terminal 7selects RU #1. Other terminals than terminals 3, 6, and 7, which havethe OBO count after the update larger than 0, cannot acquire theselection right, and wait for the next transmitted trigger frame forrandom access.

Terminals 3, 6, and 7 use RU #2, RU #4, and RU #1 to transmit frames523, 526, and 527, respectively, after elapse of a predetermined timeperiod from completion of receiving the trigger frame for random access503. Note that since RU #3 is not selected by any terminal, thetransmission is not performed at RU #3. Note that the frames transmittedby terminals 3, 6, and 7 may be an aggregation frame (A-MPDU) includingplural data frames (i.e., MPDUs or sub-frames) being aggregated.

The base station receives and decodes frames 527, 523, and 526transmitted from terminals 7, 3, and 6 by use of RU #1, RU #2 and RU #4and subjects the decoded frames to the FCS check (e.g., CRC check) todetermine whether or not the frames are successfully received. The basestation generates and transmits (downlink response) an acknowledgementresponse frame depending on check results (success or failure of thereception) of the frames. Similarly to the above description, here,Multi-STA BA frame 504 is transmitted as the single acknowledgementresponse frame which represents an acknowledgement for all the terminals3, 6, and 7. The operation of the terminal having received Multi-STA BAframe 504 is the same as in the case of Multi-STA BA frame 502.

The value of at least one of CWO max or CWO min may be notified by meansof the beacon frame, the trigger frame (including the trigger frame forrandom access) or the like from the base station to the terminalsbelonging to the BSS. In the case of notifying through the triggerframe, the common information field, the terminal information field orthe other field may be provided with a field set to at least one of theCWO max or CWO min. The initial value of the CWO (CWOinit) may also benotified in the same way, or may be defined beforehand in the system orby the standard.

Differences between the update of the CWO value according to theembodiment and the update of the contention window (CW) used for arandom backoff mechanism for the CSMA/CA is described. Assume a terminalperforms the backoff (carrier sense) by way of the CSMA/CA during a timeperiod based on the CW and performs transmission with the carrier sensebeing idle. At this time, if the transmission of the terminal isincidentally made simultaneously with transmission of another terminal,the terminal determines that the ACK is not responded due to the ACKTimeout and exponentially increases a CW value. An initial value of theCW value is CW min, and the CW value is increased up to the CW max asretransmission is performed. This is a measure for giving a furtherdispersion on a temporal axis in order to avoid the simultaneoustransmission, on the basis of a determination that the CW value usedagainst competing terminals does not give sufficient dispersion. Incontrast to this, in the scheme of the trigger frame for random accessaccording to the embodiment, there are two kinds of terminals that isone successful in acquiring the STA-unspecified RU and the otherunsuccessful among the plural terminals acquiring the selection right atthe same time (in the random backoff mechanism for the CSMA/CA, allterminals which perform transmission at the same time point basicallyfail in the transmission (the ACK is not responded)). This issignificantly different from the random backoff mechanism on thetemporal axis. In this case, giving, to the terminal which wassuccessful in acquiring the STA-unspecified RU and the terminal whichwas unsuccessful, the same condition for acquiring STA-unspecified RU atthe next trigger frame for random access may lack fairness. Therefore,in the embodiment, the CWO value of the terminal having failed in theacquisition is decreased every transmission failure to put a higherpriority for the acquisition than on the terminal having succeeded inthe acquisition, keeping the fairness between the terminals.

In the embodiment described above, the acknowledgement response frame(Multi-STA BA frame) is transmitted as the downlink response to theplural terminals having succeeded in the transmission (random access),but an embodiment may be conceivable in which the ordinary trigger frameis transmitted instead of transmitting the acknowledgement responseframe. An exemplary sequence in this case is shown in FIG. 17.

Multi-STA BA frames 507 and 504 in FIG. 14 are replaced with triggerframes 541 and 542. Trigger frames 541 and 542 in this case specifyterminals assigned for each resource unit. A format of the trigger frameis basically that shown in FIG. 9, and the structure of the commoninformation field or the terminal information field or the both of thesemay be different from that of the trigger frame for random access. Theterminals specified in trigger frame 541 or 542 use the resource unitsallocated to their own terminals to transmit the frames (here, it isassumed that the frame is the data frame) by way of the uplinktransmission after elapse of a predetermined time period from completionof receiving the trigger frame 541 or 542. Each of the frames totransmit may be an aggregation frame including plural data frames (MPDUsor sub-frames) being aggregated.

The base station, in a case of transmitting trigger frame 541 or 542,may specify the terminal(s) which succeeded in the transmission by therandom access to trigger frame for random access 501 or 503. By doingso, the terminal having succeeded in the transmission can detect thesuccess in the random access to trigger frame for random access 501 or503 on the basis of its own terminal to be specified in trigger frame541 or 542. Of the terminals having performed the random access, theterminal not specified in trigger frame 541 or 542 can determine thatits own terminal failed in the transmission. The frame transmitted bythe random access may be a frame requesting its own terminals to bespecified (i.e., allocated a resource unit) in trigger frame 541 or 542.Note that trigger frame 541 or 542 may limit the terminals to thosehaving not performed the random access and/or to those having failed inthe transmission. Trigger frame 541 or 542 may further include, besidesthe information specifying the resource units and the terminals,information required for the transmission by the terminal (packetlength, transmission power, MCS, or the like). Note that processing onthe selection of the terminal specified in the trigger frame may be madeby the MAC processor 10 (e.g., the MAC common processor 20, thereception processor 40, or the transmission processor 30), or theMAC/PHY manager 60.

Modification Example 1 of CWO Update

In the embodiment described above, the CWO value of the terminal isdecreased each time the terminal fails in transmission, but in amodification example 1, in addition to the above, the CWO value isincreased each time the transmission has succeeded wherein the initialvalue of the CWO (CWOinit) is defined between the CWO min and the CWOmax. The value of the CWOinit may be notified by means of the beaconframe, the trigger frame or the like from the base station to theterminals.

An operation according to the modification example 1 is schematicallyshown in FIG. 18. First, the value of the CWO is set to the CWOinit. Inthis example, it is 2{circumflex over ( )}3−1=7, and this is anintermediate value between the CWO min and the CWO max (intermediatevalue of the exponent part). In case of success, a stage is raised byone (exponent part P is added by 1), and in the case of failure, thestage is returned by one (the exponent part P is subtracted by 1). Aspecific example is shown below.

At the beginning 7

-   -   -<transmission success>→15        -   -<further transmission success>→31        -   -<transmission failure>→7    -   -<transmission failure>→3

Modification Example 2 of CWO Update

The initial CWOinit is started from the CWO min. In the case oftransmission failure, the CWO is kept, and in the case of transmissionsuccess, the CWO is gradually increased up to the CWO max for everytransmission success. An operation according to a modification example 2is schematically shown in FIG. 19.

First, the value of the CWO is set to the CWO min (2{circumflex over( )}3−1=7 in this case). In the case of success, the stage is raised byone (exponent part P is added by 1) and in the case of failure, the CWOvalue is kept (the value of the exponent part P is kept). A concreteexample is shown below.

At the beginning 7

-   -   -<transmission success>→15        -   <further transmission success>→31        -   -<transmission failure>→15    -   <transmission failure>→7

This method is similar to the method of deciding the CW in the randombackoff mechanism for the CSMA/CA, but different in the following point.In the modification example 2, the CWO value is increased every success,whereas in the random backoff mechanism for the CSMA/CA, the CW isincreased every failure. Therefore, both are inverse in the operation ofsuccess and failure.

Modification Example 3 of CWO Update

A modification example 3 is used in combination with the above describedembodiments and the first to second modification examples. In themodification example 3, when the same determination (success or failure)is made continuously N times, the CWO value is changed. Otherwise, thesame CWO is kept. A value of N may be notified by means of the beaconframe, the trigger frame or the like from the base station to theterminals belonging to the BSS. As an example, N may be 2 or 3 or more.

For example, in a case where the modification example 3 is combined withthe embodiment in which the CWO is decreased in the case of failure, theCWO value is decreased if the failure continuously occurred N times. Ifthe continuous failure is interrupted (if the success is made) before itreaches N times, the CWO value is not changed. In a case of thecombination with the embodiment in which the CWO is increased in thecase of success, the CWO value is increased if the success continuouslyoccurred N times. If the continuous success is interrupted (if thefailure is made) before it reaches N times, the CWO value is notchanged.

Modification Example 4 of CWO Update

As an operation of the base station, a time interval until the nexttrigger frame for random access (TF-R) is transmitted is notified astarget transmission time, for example, by means of the beacon frame. Thenext trigger frame for random access subsequently further notifieswhether or not the trigger frame for random access is transmitted. Forexample, a more data field in the Frame Control field is used as aCascaded Indication bit, and the bit is set to 1 in a case of notifyingthat a subsequent trigger frame for random access exists (is scheduled).The bit is set to 0 in a case of notifying that a subsequent triggerframe for random access does not exist (is not scheduled). The CascadedIndication bit may be provided in the common information field, theterminal information field, or a reserved field of MAC header in thetrigger frame for random access.

An exemplary sequence of the operation of the base station according tothis modification example is shown in FIG. 20. Beacon frame 551 is usedto notify a time interval until the next trigger frame for random access561 as the target transmission time. For example, an information elementfor notifying the target transmission time may be newly defined. Intrigger frame for random access 561, the Cascaded Indication bit is setto 1 because a subsequent trigger frame for random access 562 isscheduled to be transmitted. In trigger frame for random access 562, theCascaded Indication bit is set to 1 because a subsequent trigger framefor random access 563 is scheduled. In trigger frame for random access563, the Cascaded Indication bit is set to 0 because no subsequenttrigger frame for random access is scheduled. Note that in FIG. 20 otherframes transmitted by the base station (e.g., Multi-STA BA frame) arenot shown.

In the sequence like this, if the trigger frame for random access isreceived with the Cascaded Indication bit being set to 1 (the nexttrigger frame for random access is subsequent), the terminal updates theCWO value in accordance with the above embodiments or modificationexamples as needed. If the trigger frame for random access is receivedwith the Cascaded Indication bit being set to 0 (a time interval untilthe next trigger frame for random access is received is considered to berelatively long), the terminal resets the CWO value to be returned tothe initial value (CWOinit). In this exemplary sequence, in a case wherethere is a terminal in a power saving mode, the terminal having receivedthe beacon frame 551 may detect a time interval until the next triggerframe for random access 561 is transmitted to transit to the sleep modefor the time interval. In addition, the terminal, after receivingtrigger frame for random access 563 with the Cascaded Indication bitbeing set to 0, may perform the random access to the trigger frame forrandom access 563 as needed, and thereafter, transit to the sleep mode.Note that this modification example is also applicable to the terminalwhich is not in the power saving mode. This modification example can beused in combination with the above described embodiments or othermodification examples.

Modification Example 5 of CWO Update

In a case where the base station determines that many terminals fail inthe transmission of the response (UL-OFDMA) to the trigger frame forrandom access, the base station may transmit an instruction to forciblyreturn the CWO value to the CWO max or the CWOinit. For example, a bit(field) for notification may be defined in the trigger frame for randomaccess and the instruction to return the CWO value to the CWO max or theinitial value (CWOinit) is given by means of the bit. The bit may beprovided in the common information field or the terminal informationfield, or may be provided in a reserved field within the existing field.In the case where an instructed terminal, even if failing in thetransmission, receives the next trigger frame for random access with thebit for notification being set to 1, the terminal returns the CWO to theCWOinit or the CWO max (to which of the CWOinit or the CWO max to returnmay be determined beforehand or a bit indicating which of the CWOinit orthe CWO max to select may be added). A timing for returning the CWOvalue to the CWO max or the CWOinit may be a timing for updating the CWOvalue next time (timing at succeeding or failing in the transmission),or the CWO value may be immediately changed to re-obtain the backoffcount (OBO count) using the changed CWO value. Note that as anotherexample, an instruction to inhibit terminals from decreasing the CWOvalue may be also considered. Adjusting the CWO value as in thismodification example can disperse the timings of the random access bythe terminals. Note that it may be an instruction to return the CWOvalue to other value than the CWO max and the CWOinit, for example, amiddle value between the CWO max and the CWO min. The instruction toreturn the CWO value to the CWO max, the CWOinit or the like may beapplied to commonly both of the terminals having failed in thetransmission and the terminals having succeeded or only to at leasteither side of the terminals. In the latter case, a notification field(i.e., a field for notification) for the terminals having failed in thetransmission and a notification field for the terminals having succeededin the transmission may be defined to set different instructions tochange the CWO value respectively.

Here, the determination by the base station that many terminals fail inthe transmission may be made in a case where the number of the failedterminals or the number of the resource units having failed in thetransmission is equal to or more than a threshold. Alternatively, it maybe made in a case where a ratio of the number of the resource unitshaving failed in the reception to the number of STA-unspecified RUswhich are specified in the trigger frame for random access (or the totalnumber of the resource units having succeeded or failed in thereception) is equal to or more than a threshold, or other method may beused. This modification example can be used in combination with theabove described embodiments or other modification examples.

Modification Example 6 of CWO Update

In a case where no downlink transmission response (the acknowledgementresponse frame such as the Multi-STA BA frame) is received from the basestation after the terminal transmits the response to the trigger framefor random access (random access), the CWO may be returned to the CWOmax or the initial value (CWOinit). In such a case, since many terminalsare possibly determined to fail in the transmission, changing the CWOvalue in this way can disperse the timings of the random access by theterminals. Note that the CWO value may be kept as it is, instead ofreturning the CWO value to the CWO max or the initial value (CWOinit).This modification example can be used in combination with the abovedescribed embodiments or other modification examples.

Note that also in a case where although the ordinary trigger frame (see541 and 542 in FIG. 17) is transmitted as the downlink response, onlythe terminal already specified in the trigger frame for random access(as described in the above, a terminal may be specified for a resourceunit except the STA-unspecified RU in the trigger frame for randomaccess) is specified in the ordinary trigger frame, the terminal mayoperate similarly to the case of with no downlink response from the basestation. Additionally, in a case where the terminal specified in thetrigger frame for random access does not exist or no uplink transmissionis transmitted from the terminal specified in the trigger frame forrandom access, the ordinary trigger frame may not transmitted from thebase station in some cases. In such a case also, the operation may bemade similarly to the case of with no downlink response.

The terminal may operate as below. If the downlink response (e.g.,Multi-STA BA frame) is transmitted from the base station, the number ofthe terminals having succeeded in the transmission by use of theSTA-unspecified RU is counted. In the case of the terminal having failedin the transmission, its CWO value may be decreased, for example, if thenumber of the terminals having succeeded is equal to or more than athreshold or a ratio of the terminals having succeeded to the number ofSTA-unspecified RUs is equal to or more than a threshold. Alternatively,the downlink response frame transmitted from the base station may beprovided with a notification bit instructing to decrease the CWO value,and the base station may instruct to decrease the CWO value by way ofthe bit. In this case, the terminal decreases the CWO value inaccordance with the bit. The method of decreasing the CWO may conform tothe above described embodiments or modification examples.

(Modification Example of Operation in Transmission Failure)

The terminal may keep the OBO count (OBO count before subtracting thenumber of STA-unspecified RUs) which was used in the failed transmissionby use of the STA-unspecified RU, and use the kept OBO count for thenext trigger frame for random access.

On the other hand, the base station may determine whether or not manyterminals fail in the transmission of the response (UL-OFDMA) to thetrigger frame for random access, and, if determining that many terminalsfail, increase the number of STA-unspecified RUs in the next triggerframe for random access. This considers a probability that the terminalto newly acquire the selection right is additionally provided.Alternatively, the trigger frame for random access may be defined andtransmitted which specifies only the terminals having failed in thetransmission to be random-accessed. For example, a notification bitspecifying only the terminals having failed in the transmission to berandom-accessed may be provided in the common information field, theterminal information field, or the MAC header, and the trigger frame forrandom access with the notification bit being set is transmitted. Thenotification bit may be a reserved field within any field of the MACheader or may reuse one of the used fields for this purpose.

(Modification Example of Operation in Transmission Success)

The base station may put, with respect to the terminal having succeededtransmission in random access, a limitation on the number of times ofwaiting or waiting time period in view of allowing to respond(random-accessing) to the next and subsequent trigger frames for randomaccess.

This information of the limitation may be notified together with theinformation on the terminal having succeeded in the reception (e.g., BA)by way of the notification field for the terminal having succeeded, inthe downlink response by the base station after receiving the response(UL-OFDMA) to the trigger frame for random access. In a case where thedownlink response has a BA format (in a case such as where the Multi-STABA frame is used), the notification field may be structured using areserved field within the frame of the BA format or reusing one of theused fields. If the trigger frame is used as the downlink response, thenotification field may be provided in the common information field, theterminal information field, the MAC header or the like. Assume that, inthis trigger frame, the above terminal having succeeded in thetransmission is specified as a target to the UL-OFDMA.

If the terminal detects that it succeeded in the transmission on thebasis of that there is an acknowledgement to the terminal or theterminal is specified in the downlink response frame, the terminaldetects the limitation set on the number of times of waiting or thewaiting time period from the notification field of the downlink responseframe to operate so as to refrain from the transmission (random access)while the limitation is applied.

In a case where the limitation is on the number of times of waiting, theterminal decrements the number every time it receives a trigger framefor random access, and, from when receiving a trigger frame for randomaccess after the number of times of waiting reaches 0, it starts theoperation regarding the random access (e.g., the process of subtractingthe number of STA-unspecified RUs from the OBO count). In a case wherethe limitation is on the waiting time period, the terminal stands byduring the specified time period, and thereafter, from when receiving atrigger frame for random access, starts the operation regarding therandom access.

While the above limitation is applied, the OBO count when the terminalsucceeded in the transmission immediately before (OBO count beforesubtracting the number of STA-unspecified RUs) is kept, and, whenreceiving a trigger frame for random access after the limitation isreleased, the terminal subtracts the number of STA-unspecified RUs fromthe kept OBO count and when the OBO count reaches 0, it acquires theselection right and performs the random access. Note that the OBO countmay not be necessarily kept, and a new OBO count may be re-obtained fromthe current CWO.

(Modification Example of Response Method at Base Station)

The base station measures a quality of reception from a terminal whichsucceeded in the transmission in response to the trigger frame forrandom access concerning the resource unit by use of which thetransmission is performed. Examples of the reception quality include areception RSSI (Received Signal Strength Indicator) or a reception EVM(Error Vector Magnitude), but not limited thereto. For example, an SNratio (Signal to Noise Ratio; SNR) may be used. The base stationdetermines whether or not a measured value is equal to or more or lessthan a threshold depending on a used index to determine whether or notthe reception quality satisfies a criterion required for the response(is good or bad).

The base station determines, for a terminal bad in the receptionquality, that the radiowave environment of the terminal by use of theresource unit is bad, and does not perform the downlink response (thatis, does not include the acknowledgement for the terminal in theMulti-STA BA frame, or does not specify the terminal in the triggerframe (see FIG. 17), and so on). This makes the terminal to determinethat the transmission (random access) failed. Note that the base stationmay perform the downlink response even to the terminal bad in thereception quality with the downlink response frame having added theretoinformation identifying the reception quality at this time. Theterminal, in the case of determining that the reception quality at thebase station is bad on the basis of the downlink response frame althoughit succeeded in the transmission, may select another resource unit nexttime. The base station may notify the information identifying thereception quality using a reserved field within the frame of the BAformat or may reuse one of the used fields in the frame for thispurpose.

Here, the terminal may selectively notify to the base station whetherthe terminal wants that the base station responds regardless of thereception quality in the case where the base station succeeded in thereception or the terminal wants that the base station does not respondif the reception quality is bad. The MAC header or the like of the frametransmitted from the terminal may be provided with a request bit(request field) which may be set to 1 in the case of wanting the basestation not to respond if the reception quality is bad and may be set to0 in the case of wanting the base station to respond regardless of thereception quality. A relationship between 1 and 0 of the bit may beinverted. The base station may switch the response operation in the caseof having succeeded in the reception depending on the request bitincluded in the frame.

(Modification Example of Specifying Range of Random Number and SelectingSTA-Unspecified RU)

In the above described embodiments and modification examples, theterminal, which acquires the selection right when the OBO count is below0 as a result of subtracting the number of STA-unspecified RUs from theOBO count, selects any resource unit from among STA-unspecified RUs. Forexample, the resource unit is selected randomly. In this modificationexample, the resource unit to be selected is decided depending on theOBO count at a time of waiting for the trigger frame for random access.For example, when the trigger frame for random access is received in astate where the OBO count is 3, and if the number of STA-unspecified RUsis 4, the OBO count becomes 3−4=−1(−>0) and the terminal acquires theselection right. In this case, because the OBO count while waiting is 3,the resource unit corresponding to 3 (e.g., RU #3) is selected. Thevalue of the OBO may be associated with the resource unit beforehand.One value may be associated with the plural resource units. In thiscase, a resource unit may be selected from the associated pluralresource units randomly.

As another example, every time the trigger frame for random access isreceived, the CWO is set which is M times (M is an integer larger than0) the number of STA-unspecified RUs. In other words, the CWO is setdepending on the number of STA-unspecified RUs. For example, if thenumber of STA-unspecified RUs is 4 and M is 2, it is CWO=8. Then, arandom number (OBO count) is selected from a range between 0 and(CWO−1). If the selected random number has a value equal to or less thana value obtained by subtracting 1 from the number of STA-unspecified RUs(i.e., “number of STA-unspecified RUs−1”), the selection right isacquired and the resource unit is selected from STA-unspecified RUs. The“number of STA-unspecified RUs−1” is an example, and the number ofSTA-unspecified RUs or another value may be used. The resource unit maybe selected in accordance with an association in which the OBO count isassociated with the resource unit beforehand. However, the selection maybe made randomly. After the terminal transmits based on the selectedresource unit, the terminal may adjust the M value from the initialvalue depending on whether the transmission has succeeded or not. The Mvalue may be adjusted in a range between a minimum value and a maximumvalue which may be defined respectively. The adjustment method of the Mvalue may be similar to the way of changing the CWO in the abovedescribed embodiments and modification examples. Decreasing the CWOcorresponds to decreasing the M value and increasing the CWO correspondsto increasing the M value. Note that the setting of the CWO depending onthe number of STA-unspecified RUs described in this paragraph may beapplied to other modification examples.

The M value (at least one of initial value, minimum value, or maximumvalue) may be notified by means of the beacon frame, the trigger frame(including the trigger frame for random access) or the like to theterminals. An information element notifying the M value may be set inthe beacon frame, or a reserved field within any field of the beaconframe may be used to set the M value. The common information field orthe terminal information field of the trigger frame may be provided witha field notifying the M value, or a reserved field in the MAC header maybe used or one of the used fields in the MAC header may be reused tonotify the M value.

Other Modification Examples

In the above described embodiments and modification examples, theterminal having failed in transmission autonomously makes thedetermination to adjust the CWO value, but the base station may instructthe terminal to adjust the CWO value. As an example, in the triggerframe (see 541 and 542 in FIG. 14), in addition to the informationspecifying the terminal for each resource unit, information concerningthe adjustment method of the CWO is set in at least one of thenotification field for the terminal having failed in the transmission orthe notification field for the terminal having succeeded in thetransmission. In the adjustment method, the instructions are set such asto decrease the CWO, increase the CWO, return the CWO to the initialvalue, set the CWO to the maximum value, or set the CWO to the minimumvalue. When the instruction is to decrease or increase the CWO, theadjustment method may be decided similar to the way of operation at theterminal described above. The notification field may be provided in thecommon information field or the terminal information field of thetrigger frame or both of them. Alternatively, a reserved field withinany field of the MAC header or the like may be used or one of the usedfields in the MAC header may be reused to form the notification field.For example, if the terminal detects that its own terminal is notspecified in the trigger frame (see 541 and 542 in FIG. 14), theterminal updates the CWO value in accordance with the adjustment methodspecified in the notification field for the terminal having failed.

FIG. 21 is a diagram showing an exemplary flowchart of the operation ofthe terminal according to the embodiment of the invention. The terminalreceives from the base station a trigger frame (trigger frame for randomaccess) specifying plural STA-unspecified RUs (resource unit for randomaccess) (S101). The frame may specify that a part of the resource unitsexcept the STA-unspecified RUs are used by specific terminals. Theterminal subtracts the number of STA-unspecified RUs which is specifiedin the trigger frame for random access from the backoff count (OBOcount) selected from a range not more than the CWO value, and checkswhether or not a value after the subtraction reaches a predeterminedvalue (e.g., 0) (S102). If reaching a predetermined value, the terminaldetermines that the selection right to the STA-unspecified RU isacquired (YES), and if not reaching a predetermined value, the terminaldetermines that the selection right is not acquired (NO). Note that thesubtraction may not be necessarily performed in fact, and as describedabove, for example, it may be determined whether or not the selectionright is acquired on the basis of a magnitude relationship between theOBO count when the trigger frame for random access is received and thenumber of STA-unspecified RUs. The terminal, if acquiring the selectionright, uses an arbitrary resource unit selected from STA-unspecified RUsto transmit the frame (S104). The type of frame transmitted may bearbitrary or may be a kind defined beforehand (for example, thetransmitted frame may be a frame notifying a presence or absence of theuplink transmission request, and so on). The operation described here ismerely an example, and various operations may be made depending on theabove described embodiments and modification examples.

FIG. 22 is a diagram showing an exemplary flowchart of the operation ofthe base station according to the embodiment of the invention.

The base station transmits a trigger frame (trigger frame for randomaccess) specifying plural STA-unspecified RUs (resource unit for randomaccess) (S201). The frame may specify that a part of the resource unitsexcept the STA-unspecified RUs are used by specific terminals. The basestation determines whether or not the response frames to the triggerframe for random access are received by use of the STA-unspecified RUswhich are specified in the trigger frame for random access within apredetermined time period from the transmission (S202). Morespecifically, the base station decodes the wireless signals received byuse of STA-unspecified RUs to check whether or not frames aresuccessfully received. The base station transmits a frame including theinformation on the terminals from which the frames were successfullyreceived in downlink (S203). The frame may be a Multi-STA BA frame ormay be a trigger frame in which the terminals are assigned for theresource units to be used, as described above. In the latter case of thetrigger frame, the terminals from which reception are succeeded isspecified in the trigger frame. The downlink-transmitted frames mayinclude information on a value range (CWO value) for the terminal tocontrol determination on whether to respond (whether to perform therandom access) to the trigger frame for random access. As an example,the number of terminals having succeeded in the transmission (the numberof resource units by use of which the frames are successfully received)may be detected, and the downlink-transmitted frames may includeinformation concerning the CWO value which is determined depending onthe number of terminals (or the number of resource units). The examplesof the information concerning the CWO value include instructioninformation to set the CWO value to an initial value, a minimum value,or an maximum value. The information concerning the CWO value may be setin notification fields respectively for the terminals having succeededand the terminals having failed in transmission. Alternatively, anotification field for either one side of the terminals having succeededand the terminals having failed may be defined to be set therein.Besides, the downlink-transmitted frames may include the informationdescribed in the above modification examples.

As described above, according to the embodiment of the presentinvention, the CWOs of the terminals are individually adjusted dependingon the failure or success in the transmission responding to the triggerframe for random access, giving an opportunity of fair transmission(random access) between the terminals.

The embodiment describes the random access in the case of carrying outthe UL-OFDMA to the trigger frame for random access, but may beapplicable to the random access also in a case of another communicationscheme combining the UL-OFDMA and the uplink MU-MIMO (UL-MU-MIMO)(UL-OFDMA & UL-MU-MIMO). In the UL-MU-MIMO, the plural terminalssimultaneously transmit the frames at the same frequency band to thebase station (spatial multiplexing transmission) to give high-efficiencyof the uplink transmission. Preamble signals orthogonal to each otherare included in the physical headers of the frames transmitted from theplural terminals such that the base station can estimate an uplinkchannel response with each of the terminals on the basis of thesepreamble signals and separate these frames. In the UL-OFDMA & MU-MIMO,the plural terminals uses, for each of the resource units, the sameresource unit to perform the MU-MIMO transmission. At this time, theplural terminals using the same resource unit use the preamble signalsdifferent from each other to perform the transmission. The embodimentsare also applicable to the scheme like this.

Second Embodiment

FIG. 23 is a functional block diagram of a base station (access point)400 according to a second embodiment. The access point includes acommunication processor 401, a transmitter 402, a receiver 403, antennas42A, 42B, 42C, and 42D, a network processor 404, a wired I/F 405, and amemory 406. The access point 400 is connected to a server 407 throughthe wired I/F 405. The communication processor 401 has functions similarto the MAC processor 10 and the MAC/PHY manager 60 described in thefirst embodiment. The transmitter 402 and the receiver 403 havefunctions similar to the PHY processor 50 and the analog processor 70described in the first embodiment. The network processor 404 hasfunctions similar to the higher processor 90 described in the firstembodiment. The communication processor 401 may internally possess abuffer for transferring data to and from the network processor 404. Thebuffer may be a volatile memory, such as an SRAM or a DRAM, or may be anon-volatile memory, such as a NAND or an MRAM.

The network processor 404 controls data exchange with the communicationprocessor 401, data writing and reading to and from the memory 406, andcommunication with the server 407 through the wired I/F 405. The networkprocessor 404 may execute a higher communication process of the MAClayer, such as TCP/IP or UDP/IP, or a process of the application layer.The operation of the network processor may be performed throughprocessing of software (program) by a processor, such as a CPU. Theoperation may be performed by hardware or may be performed by both ofthe software and the hardware.

For example, the communication processor 401 corresponds to a basebandintegrated circuit, and the transmitter 402 and the receiver 403correspond to an RF integrated circuit that transmits and receivesframes. The communication processor 401 and the network processor 404may be formed by one integrated circuit (one chip). Parts that executeprocessing of digital areas of the transmitter 402 and the receiver 403and parts that execute processing of analog areas may be formed bydifferent chips. The communication processor 401 may execute a highercommunication process of the MAC layer, such as TCP/IP or UDP/IP.Although the number of antennas is four here, it is only necessary thatat least one antenna is included.

The memory 406 saves data received from the server 407 and data receivedby the receiver 402. The memory 406 may be, for example, a volatilememory, such as a DRAM, or may be a non-volatile memory, such as a NANDor an MRAM. The memory 406 may be an SSD, an HDD, an SD card, an eMMC,or the like. The memory 406 may be provided outside of the base station400.

The wired I/F 405 transmits and receives data to and from the server407. Although the communication with the server 407 is performed througha wire in the present embodiment, the communication with the server 407may be performed wirelessly. In this case, a wireless I/F may beemployed instead of the wired I/F 405.

The server 407 is a communication apparatus that returns a responseincluding requested data in response to reception of a data forwardrequest for requesting transmission of the data. Examples of the server407 include an HTTP server (Web server) and an FTP server. However, theserver 407 is not limited to these as long as the server 407 has afunction of returning the requested data. The server 407 may be acommunication apparatus operated by the user, such as a PC or asmartphone.

When the STA belonging to the BSS of the base station 400 issues aforward request of data for the server 407, a packet regarding the dataforward request is transmitted to the base station 400. The base station400 receives the packet through the antennas 42A to 42D. The basestation 400 causes the receiver 403 to execute the process of thephysical layer and the like and causes the communication processor 401to execute the process of the MAC layer and the like.

The network processor 404 analyzes the packet received from thecommunication processor 401. Specifically, the network processor 404checks the destination IP address, the destination port number, and thelike. When the data of the packet is a data forward request such as anHTTP GET request, the network processor 404 checks whether the datarequested by the data forward request (for example, data in the URLrequested by the HTTP GET request) is cached (stored) in the memory 406.A table associating the URL (or reduced expression of the URL, such as ahash value or an identifier substituting the URL) and the data is storedin the memory 406. The fact that the data is cached in the memory 406will be expressed that the cache data exists in the memory 406.

When the cache data does not exist in the memory 406, the networkprocessor 404 transmits the data forward request to the server 407through the wired I/F 405. In other words, the network processor 404substitutes the STA to transmit the data forward request to the server407. Specifically, the network processor 404 generates an HTTP requestand executes protocol processing, such as adding the TCP/IP header, totransfer the packet to the wired I/F 405. The wired I/F 405 transmitsthe received packet to the server 407.

The wired I/F 405 receives, from the server 407, a packet that is aresponse to the data forward request. From the IP header of the packetreceived through the wired I/F 405, the network processor 404 figuresout that the packet is addressed to the STA and transfers the packet tothe communication processor 401. The communication processor 401executes processing of the MAC layer and the like for the packet. Thetransmitter 402 executes processing of the physical layer and the likeand transmits the packet addressed to the STA from the antennas 42A to42D. The network processor 404 associates the data received from theserver 407 with the URL (or reduced expression of the URL) and saves thecache data in the memory 406.

When the cache data exists in the memory 406, the network processor 404reads the data requested by the data forward request from the memory 406and transmits the data to the communication processor 401. Specifically,the network processor 404 adds the HTTP header or the like to the dataread from the memory 406 and executes protocol processing, such asadding the TCP/IP header, to transmit the packet to the communicationprocessor 401. In this case, the transmitter IP address of the packet isset to the same IP address as the server, and the transmitter portnumber is also set to the same port number as the server (destinationport number of the packet transmitted by the communication terminal),for example. Therefore, it can be viewed from the STA as ifcommunication with the server 407 is established. The communicationprocessor 401 executes processing of the MAC layer and the like for thepacket. The transmitter 402 executes processing of the physical layerand the like and transmits the packet addressed to the STA from theantennas 42A to 42D.

According to the operation, frequently accessed data is responded basedon the cache data saved in the memory 406, and the traffic between theserver 407 and the base station 400 can be reduced. Note that theoperation of the network processor 404 is not limited to the operationof the present embodiment. There is no problem in performing otheroperation when a general caching proxy is used, in which data isacquired from the server 407 in place of the STA, the data is cached inthe memory 406, and a response is made from the cache data of the memory406 for a data forward request of the same data.

The base station (access point) of the present embodiment can be appliedas the base station of the first embodiment. In this case, thetransmission of the frame, the data or the packet used in the firstembodiment may be carried out based on the cached data stored in thememory 406. Also, information obtained based on the frame, the data orthe packet received by the base station in the first embodiment may becached in the memory 406. The frame transmitted by the base station inthe first embodiment may include the cached data or information based onthe cached data. The information based on the cached data may includeinformation on existence or non-existence of data addressed to theterminal, information on a size of the data, or information on a size ofa packet required for transmission of the data. The information based onthe cached data may include a modulation scheme required fortransmission of the data etc.

In the present embodiment, although the base station with the cachefunction is described, a terminal (STA) with the cache function can alsobe realized by the same block configuration as FIG. 23. Here, theterminal is non-AP terminal (as previously described, a base station(access point) is one mode of a wireless communication terminal). Inthis case, the wired I/F 405 may be omitted. The frame transmitted bythe terminal in the first embodiment may include the cached data orinformation based on the cached data. The information based on thecached data may include information on existence or non-existence ofdata for transmission to the terminal, information on a size of thedata, or information on a size of a packet required for transmission ofthe data. The information based on the cached data may include amodulation scheme required for transmission of the data etc.

Third Embodiment

FIG. 24 shows an example of entire configuration of a terminal or a basestation. The example of configuration is just an example, and thepresent embodiment is not limited to this. The terminal or the basestation includes one or a plurality of antennas 1 to n (n is an integerequal to or greater than 1), a wireless LAN module 148, and a hostsystem 149. The wireless LAN module 148 corresponds to the wirelesscommunication apparatus according to the first embodiment. The wirelessLAN module 148 includes a host interface and is connected to the hostsystem 149 through the host interface. Other than the connection to thehost system 149 through the connection cable, the wireless LAN module148 may be directly connected to the host system 149. The wireless LANmodule 148 can be mounted on a substrate by soldering or the like andcan be connected to the host system 149 through wiring of the substrate.The host system 149 uses the wireless LAN module 148 and the antennas 1to n to communicate with external apparatuses according to an arbitrarycommunication protocol. The communication protocol may include theTCP/IP and a protocol of a layer higher than that. Alternatively, theTCP/IP may be mounted on the wireless LAN module 148, and the hostsystem 149 may execute only a protocol in a layer higher than that. Inthis case, the configuration of the host system 149 can be simplified.Examples of the present terminal include a mobile terminal, a TV, adigital camera, a wearable device, a tablet, a smartphone, a gamedevice, a network storage device, a monitor, a digital audio player, aWeb camera, a video camera, a projector, a navigation system, anexternal adaptor, an internal adaptor, a set top box, a gateway, aprinter server, a mobile access point, a router, an enterprise/serviceprovider access point, a portable device, a hand-held device, a vehicleand so on.

The wireless LAN module 148 (or the wireless communication device) mayhave functions of other wireless communication standards such as LTE(Long Term Evolution), LTE-Advanced (standards for mobile phones) aswell as the IEEE802.11.

FIG. 25 shows an example of hardware configuration of a wireless LANmodule. The configuration can also be applied when the wirelesscommunication apparatus is mounted on either one of the terminal that isa non-base station and the base station. Therefore, the configurationcan be applied as an example of specific configuration of the wirelesscommunication apparatus shown in FIG. 1. At least one antenna 247 isincluded in the example of configuration. When a plurality of antennasare included, a plurality of sets of a transmission system (216 and 222to 225), a reception system (232 to 235), a PLL 242, a crystaloscillator (reference signal source) 243, and a switch 245 may bearranged according to the antennas, and each set may be connected to acontrol circuit 212. One or both of the PLL 242 and the crystaloscillator 243 correspond to an oscillator according to the presentembodiment.

The wireless LAN module (wireless communication apparatus) includes abaseband IC (Integrated Circuit) 211, an RF (Radio Frequency) IC 221, abalun 225, the switch 245, and the antenna 247.

The baseband IC 211 includes the baseband circuit (control circuit) 212,a memory 213, a host interface 214, a CPU 215, a DAC (Digital to AnalogConverter) 216, and an ADC (Analog to Digital Converter) 217.

The baseband IC 211 and the RF IC 221 may be formed on the samesubstrate. The baseband IC 211 and the RF IC 221 may be formed by onechip. Both or one of the DAC 216 and the ADC 217 may be arranged on theRF IC 221 or may be arranged on another IC. Both or one of the memory213 and the CPU 215 may be arranged on an IC other than the baseband IC.

The memory 213 stores data to be transferred to and from the hostsystem. The memory 213 also stores one or both of information to betransmitted to the terminal or the base station and informationtransmitted from the terminal or the base station. The memory 213 mayalso store a program necessary for the execution of the CPU 215 and maybe used as a work area for the CPU 215 to execute the program. Thememory 213 may be a volatile memory, such as an SRAM or a DRAM, or maybe a non-volatile memory, such as a NAND or an MRAM.

The host interface 214 is an interface for connection to the hostsystem. The interface can be anything, such as UART, SPI, SDIO, USB, orPCI Express.

The CPU 215 is a processor that executes a program to control thebaseband circuit 212. The baseband circuit 212 mainly executes a processof the MAC layer and a process of the physical layer. One or both of thebaseband circuit 212 and the CPU 215 correspond to the communicationcontrol apparatus that controls communication, the controller thatcontrols communication, or controlling circuitry that controlscommunication.

At least one of the baseband circuit 212 or the CPU 215 may include aclock generator that generates a clock and may manage internal time bythe clock generated by the clock generator.

For the process of the physical layer, the baseband circuit 212 performsaddition of the physical header, coding, encryption, modulation process,and the like of the frame to be transmitted and generates, for example,two types of digital baseband signals (hereinafter, “digital I signal”and “digital Q signal”).

The DAC 216 performs DA conversion of signals input from the basebandcircuit 212. More specifically, the DAC 216 converts the digital Isignal to an analog I signal and converts the digital Q signal to ananalog Q signal. Note that a single system signal may be transmittedwithout performing quadrature modulation. When a plurality of antennasare included, and single system or multi-system transmission signalsequivalent to the number of antennas are to be distributed andtransmitted, the number of provided DACs and the like may correspond tothe number of antennas.

The RF IC 221 is, for example, one or both of an RF analog IC and a highfrequency IC. The RF IC 221 includes a filter 222, a mixer 223, apreamplifier (PA) 224, the PLL (Phase Locked Loop) 242, a low noiseamplifier (LNA) 234, a balun 235, a mixer 233, and a filter 232. Some ofthe elements may be arranged on the baseband IC 211 or another IC. Thefilters 222 and 232 may be bandpass filters or low pass filters. The RFIC 221 is connected to the antenna 247 through the switch 245.

The filter 222 extracts a signal of a desired band from each of theanalog I signal and the analog Q signal input from the DAC 216. The PLL242 uses an oscillation signal input from the crystal oscillator 243 andperforms one or both of division and multiplication of the oscillationsignal to thereby generate a signal at a certain frequency synchronizedwith the phase of the input signal. Note that the PLL 242 includes a VCO(Voltage Controlled Oscillator) and uses the VCO to perform feedbackcontrol based on the oscillation signal input from the crystaloscillator 243 to thereby obtain the signal at the certain frequency.The generated signal at the certain frequency is input to the mixer 223and the mixer 233. The PLL 242 is equivalent to an example of anoscillator that generates a signal at a certain frequency.

The mixer 223 uses the signal at the certain frequency supplied from thePLL 242 to up-convert the analog I signal and the analog Q signal passedthrough the filter 222 into a radio frequency. The preamplifier (PA)amplifies the analog I signal and the analog Q signal at the radiofrequency generated by the mixer 223, up to desired output power. Thebalun 225 is a converter for converting a balanced signal (differentialsignal) to an unbalanced signal (single-ended signal). Although thebalanced signal is handled by the RF IC 221, the unbalanced signal ishandled from the output of the RF IC 221 to the antenna 247. Therefore,the balun 225 performs the signal conversions.

The switch 245 is connected to the balun 225 on the transmission sideduring the transmission and is connected to the balun 234 or the RF IC221 on the reception side during the reception. The baseband IC 211 orthe RF IC 221 may control the switch 245. There may be another circuitthat controls the switch 245, and the circuit may control the switch245.

The analog I signal and the analog Q signal at the radio frequencyamplified by the preamplifier 224 are subjected to balanced-unbalancedconversion by the balun 225 and are then emitted as radio waves to thespace from the antenna 247.

The antenna 247 may be a chip antenna, may be an antenna formed bywiring on a printed circuit board, or may be an antenna formed by usinga linear conductive element.

The LNA 234 in the RF IC 221 amplifies a signal received from theantenna 247 through the switch 245 up to a level that allowsdemodulation, while maintaining the noise low. The balun 235 performsunbalanced-balanced conversion of the signal amplified by the low noiseamplifier (LNA) 234. The mixer 233 uses the signal at the certainfrequency input from the PLL 242 to down-convert, to a baseband, thereception signal converted to a balanced signal by the balun 235. Morespecifically, the mixer 233 includes a unit that generates carrier wavesshifted by a phase of 90 degrees based on the signal at the certainfrequency input from the PLL 242. The mixer 233 uses the carrier wavesshifted by a phase of 90 degrees to perform quadrature demodulation ofthe reception signal converted by the balun 235 and generates an I(In-phase) signal with the same phase as the reception signal and a Q(Quad-phase) signal with the phase delayed by 90 degrees. The filter 232extracts signals with desired frequency components from the I signal andthe Q signal. Gains of the I signal and the Q signal extracted by thefilter 232 are adjusted, and the I signal and the Q signal are outputfrom the RF IC 221.

The ADC 217 in the baseband IC 211 performs AD conversion of the inputsignal from the RF IC 221. More specifically, the ADC 217 converts the Isignal to a digital I signal and converts the Q signal to a digital Qsignal. Note that a single system signal may be received withoutperforming quadrature demodulation.

When a plurality of antennas are provided, the number of provided ADCsmay correspond to the number of antennas. Based on the digital I signaland the digital Q signal, the baseband circuit 212 executes a process ofthe physical layer and the like, such as demodulation process, errorcorrecting code process, and process of physical header, and obtains aframe. The baseband circuit 212 applies a process of the MAC layer tothe frame. Note that the baseband circuit 212 may be configured toexecute a process of TCP/IP when the TCP/IP is implemented.

The baseband circuit 212 or the CPU 215 may execute a process regardingthe MIMO. The baseband circuit 212 or the CPU 215 may execute at leastone or a plurality of a process of propagation path estimation, atransmission weight calculation process, a separation process of stream,and the like. The baseband circuit 212 or the CPU 215 may control theoperation of the filters 222 and 232 to extract signals covered by aused channel according to the setting of the channel. Another controllerthat controls the filters 222 and 232 may exist, and the basebandcircuit 212 or the CPU 215 may issue an instruction to the controller toperform similar control.

Fourth Embodiment

FIG. 26(A) and FIG. 26(B) are perspective views of wireless terminalaccording to the fourth embodiment. The wireless terminal in FIG. 26(A)is a notebook PC 301 and the wireless communication device (or awireless device) in FIG. 26(B) is a mobile terminal 321. Each of themcorresponds to one form of a terminal (which may indicate a basestation). The notebook PC 301 and the mobile terminal 321 are equippedwith wireless communication devices 305 and 315, respectively. Thewireless communication device provided in a terminal (which may indicatea base station) which has been described above can be used as thewireless communication devices 305 and 315. A wireless terminal carryinga wireless communication device is not limited to notebook PCs andmobile terminals. For example, it can be installed in a TV, a digitalcamera, a wearable device, a tablet, a smart phone, a gaming device, anetwork storage device, a monitor, a digital audio player, a web camera,a video camera, a projector, a navigation system, an external adapter,an internal adapter, a set top box, a gateway, a printer server, amobile access point, a router, an enterprise/service provider accesspoint, a portable device, a handheld device, a vehicle and so on.

Moreover, a wireless communication device installed in a terminal (whichmay indicate a base station) can also be provided in a memory card. FIG.27 illustrates an example of a wireless communication device mounted ona memory card. A memory card 331 contains a wireless communicationdevice 355 and a body case 332. The memory card 331 uses the wirelesscommunication device 355 for wireless communication with externaldevices. Here, in FIG. 27, the description of other installed elements(for example, a memory, and so on) in the memory card 331 is omitted.

Fifth Embodiment

In the fifth embodiment, a bus, a processor unit and an externalinterface unit are provided in addition to the configuration of thewireless communication device (which may indicate the wirelesscommunication device mounted in the terminal, the wireless communicationdevice mounted in the base station or both of them) according to any ofthe above embodiments. The processor unit and the external interfaceunit are connected with an external memory (a buffer) through the bus. Afirmware operates the processor unit. Thus, by adopting a configurationin which the firmware is included in the wireless communication device,the functions of the wireless communication device can be easily changedby rewriting the firmware. The processing unit in which the firmwareoperates may be a processor that performs the process of thecommunication controlling device or the control unit according to thepresent embodiment, or may be another processor that performs a processrelating to extending or altering the functions of the process of thecommunication controlling device or the control unit. The processingunit in which the firmware operates may be included in the access pointor the wireless terminal according to the present embodiment.Alternatively, the processing unit may be included in the integratedcircuit of the wireless communication device installed in the accesspoint, or in the integrated circuit of the wireless communication deviceinstalled in the wireless terminal.

Sixth Embodiment

In the sixth embodiment, a clock generating unit is provided in additionto the configuration of the wireless communication device (which mayindicate the wireless communication device mounted in the terminal, thewireless communication device mounted in the base station or both ofthem) according to any of the above embodiments. The clock generatingunit generates a clock and outputs the clock from an output terminal tothe exterior of the wireless communication device. Thus, by outputtingto the exterior the clock generated inside the wireless communicationdevice and operating the host by the clock output to the exterior, it ispossible to operate the host and the wireless communication device in asynchronized manner.

Seventh Embodiment

In the seventh embodiment, a power source unit, a power sourcecontrolling unit and a wireless power feeding unit are included inaddition to the configuration of the wireless communication device(which may indicate the wireless communication device mounted in theterminal, the wireless communication device mounted in the base stationor both of them) according to any of the above embodiments. The powersupply controlling unit is connected to the power source unit and to thewireless power feeding unit, and performs control to select a powersource to be supplied to the wireless communication device. Thus, byadopting a configuration in which the power source is included in thewireless communication device, power consumption reduction operationsthat control the power source are possible.

Eighth Embodiment

In the eighth embodiment, a SIM card is added to the configuration ofthe wireless communication device (which may indicate the wirelesscommunication device mounted in the terminal, the wireless communicationdevice mounted in the base station or both of them) according to theabove embodiments. For example, the SIM card is connected with the MACprocessing unit 10, the MAC/PHY management unit 60 or the controllingunit 112 in the wireless communication device. Thus, by adopting aconfiguration in which the SIM card is included in the wirelesscommunication device, authentication processing can be easily performed.

Ninth Embodiment

In the ninth embodiment, a video image compressing/decompressing unit isadded to the configuration of the wireless communication device (whichmay indicate the wireless communication device mounted in the terminal,the wireless communication device mounted in the base station or both ofthem) according to any of the above embodiments. The video imagecompressing/decompressing unit is connected to the bus. Thus, byadopting a configuration in which the video imagecompressing/decompressing unit is included in the wireless communicationdevice, transmitting a compressed video image and decompressing areceived compressed video image can be easily done.

Tenth Embodiment

In the tenth embodiment, an LED unit is added to the configuration ofthe wireless communication device (which may indicate the wirelesscommunication device mounted in the terminal, the wireless communicationdevice mounted in the base station or both of them) according to any ofthe above embodiments. For example, the LED unit is connected to atleast one of the MAC processing unit 10, the MAC/PHY management unit 60,the transmission processing circuit 113, the reception processingcircuit 114 or the controlling circuit 112. Thus, by adopting aconfiguration in which the LED unit is included in the wirelesscommunication device, notifying the operation state of the wirelesscommunication device to the user can be easily done.

Eleventh Embodiment

In the eleventh embodiment, a vibrator unit is included in addition tothe configuration of the wireless communication device (which mayindicate the wireless communication device mounted in the terminal, thewireless communication device mounted in the base station or both ofthem) according to any of the above embodiments. For example, thevibrator unit is connected to at least one of the MAC processing unit10, the MAC/PHY management unit 60, the transmission processing circuit113, the reception processing circuit 114 or the controlling circuit112. Thus, by adopting a configuration in which the vibrator unit isincluded in the wireless communication device, notifying the operationstate of the wireless communication device to the user can be easilydone.

Twelfth Embodiment

In a twelfth embodiment, the configuration of the wireless communicationdevice includes a display in addition to the configuration of thewireless communication device (which may indicate the wirelesscommunication device mounted in the terminal, the wireless communicationdevice mounted in the base station or both of them) according to any oneof the above embodiments. The display may be connected to the MACprocessing unit of the wireless communication device via a bus (notshown). As seen from the above, the configuration including the displayto display the operation state of the wireless communication device onthe display allows the operation status of the wireless communicationdevice to be easily notified to a user.

Thirteenth Embodiment

In the present embodiment, [1] the frame type in the wirelesscommunication system, [2] a technique of disconnection between wirelesscommunication devices, [3] an access scheme of a wireless LAN system and[4] a frame interval of a wireless LAN are described.

[1] Frame Type in Communication System

Generally, as mentioned above, frames treated on a wireless accessprotocol in a wireless communication system are roughly divided intothree types of the data frame, the management frame and the controlframe. These types are normally shown in a header part which is commonlyprovided to frames. As a display method of the frame type, three typesmay be distinguished in one field or may be distinguished by acombination of two fields. In IEEE 802.11 standard, identification of aframe type is made based on two fields of Type and Subtype in the FrameControl field in the header part of the MAC frame. The Type field is onefor generally classifying frames into a data frame, a management frame,or a control frame and the Subtype field is one for identifying moredetailed type in each of the classified frame types such as a beaconframe belonging to the management frame.

The management frame is a frame used to manage a physical communicationlink with a different wireless communication device. For example, thereare a frame used to perform communication setting with the differentwireless communication device or a frame to release communication link(that is, to disconnect the connection), and a frame related to thepower save operation in the wireless communication device.

The data frame is a frame to transmit data generated in the wirelesscommunication device to the different wireless communication deviceafter a physical communication link with the different wirelesscommunication device is established. The data is generated in a higherlayer of the present embodiment and generated by, for example, a user'soperation.

The control frame is a frame used to perform control at the time oftransmission and reception (exchange) of the data frame with thedifferent wireless communication device. A response frame transmittedfor the acknowledgment in a case where the wireless communication devicereceives the data frame or the management frame, belongs to the controlframe. The response frame is, for example, an ACK frame or a BlockACKframe. The RTS frame and the CTS frame are also the control frame.

These three types of frames are subjected to processing based on thenecessity in the physical layer and then transmitted as physical packetsvia an antenna. In IEEE 802.11 standard (including the extended standardsuch as IEEE Std 802.11ac-2013), an association process is defined asone procedure for connection establishment. The association requestframe and the association response frame which are used in the procedureare a management frame. Since the association request frame and theassociation response frame is the management frame transmitted in aunicast scheme, the frames causes the wireless communication terminal inthe receiving side to transmit an ACK frame being a response frame. TheACK frame is a control frame as described in the above.

[2] Technique of Disconnection Between Wireless Communication Devices

For disconnection, there are an explicit technique and an implicittechnique. As the explicit technique, a frame to disconnect any one ofthe connected wireless communication devices is transmitted. This framecorresponds to Deauthentication frame defined in IEEE 802.11 standardand is classified into the management frame. The frame for disconnectionmay be referred to as “release frame” by the meaning of releasingconnection, for example. Normally, it is determined that the connectionis disconnected at the timing of transmitting the release frame in awireless communication device on the side to transmit the release frameand at the timing of receiving the release frame in a wirelesscommunication device on the side to receive the release frame.Afterward, it returns to the initial state in a communication phase, forexample, a state to search for a wireless communication device of thecommunicating partner. In a case that the wireless communication basestation disconnects with a wireless communication terminal, for example,the base station deletes information on the wireless communicationdevice from a connection management table if the base station holds theconnection management table for managing wireless communicationterminals which entries into the BSS of the base station-self. Forexample, in a case that the base station assigns an AID to each wirelesscommunication terminal which entries into the BSS at the time when thebase station permitted each wireless communication terminal to connectto the base station-self in the association process, the base stationdeletes the held information related to the AID of the wirelesscommunication terminal disconnected with the base station and mayrelease the AID to assign it to another wireless communication devicewhich newly entries into the BSS.

On the other hand, as the implicit technique, it is determined that theconnection state is disconnected in a case where frame transmission(transmission of a data frame and management frame or transmission of aresponse frame with respect to a frame transmitted by the subjectdevice) is not detected from a wireless communication device of theconnection partner which has established the connection for a certainperiod. Such a technique is provided because, in a state where it isdetermined that the connection is disconnected as mentioned above, astate is considered where the physical wireless link cannot be secured,for example, the communication distance to the wireless communicationdevice of the connection destination is separated and the radio signalscannot be received or decoded. That is, it is because the reception ofthe release frame cannot be expected.

As a specific example to determine the disconnection of connection in animplicit method, a timer is used. For example, at the time oftransmitting a data frame that requests an acknowledgment responseframe, a first timer (for example, a retransmission timer for a dataframe) that limits the retransmission period of the frame is activated,and, if the acknowledgement response frame to the frame is not receiveduntil the expiration of the first timer (that is, until a desiredretransmission period passes), retransmission is performed. When theacknowledgment response frame to the frame is received, the first timeris stopped.

On the other hand, when the acknowledgment response frame is notreceived and the first timer expires, for example, a management frame toconfirm whether a wireless communication device of a connection partneris still present (in a communication range) (in other words, whether awireless link is secured) is transmitted, and, at the same time, asecond timer (for example, a retransmission timer for the managementframe) to limit the retransmission period of the frame is activated.Similarly to the first timer, even in the second timer, retransmissionis performed if an acknowledgment response frame to the frame is notreceived until the second timer expires, and it is determined that theconnection is disconnected when the second timer expires.

Alternatively, a third timer is activated when a frame is received froma wireless communication device of the connection partner, the thirdtimer is stopped every time the frame is newly received from thewireless communication device of the connection partner, and it isactivated from the initial value again. When the third timer expires,similarly to the above, a management frame to confirm whether thewireless communication device of the connection party is still present(in a communication range) (in other words, whether a wireless link issecured) is transmitted, and, at the same time, a second timer (forexample, a retransmission timer for the management frame) to limit theretransmission period of the frame is activated. Even in this case,retransmission is performed if an acknowledgment response frame to theframe is not received until the second timer expires, and it isdetermined that the connection is disconnected when the second timerexpires. The latter management frame to confirm whether the wirelesscommunication device of the connection partner is still present maydiffer from the management frame in the former case. Moreover, regardingthe timer to limit the retransmission of the management frame in thelatter case, although the same one as that in the former case is used asthe second timer, a different timer may be used.

[3] Access Scheme of Wireless LAN System

For example, there is a wireless LAN system with an assumption ofcommunication or competition with a plurality of wireless communicationdevices. CSMA/CA is set as the basis of an access scheme in IEEE802.11(including an extension standard or the like) wireless LAN. In a schemein which transmission by a certain wireless communication device isgrasped and transmission is performed after a fixed time from thetransmission end, simultaneous transmission is performed in theplurality of wireless communication devices that grasp the transmissionby the wireless communication device, and, as a result, radio signalscollide and frame transmission fails. By grasping the transmission bythe certain wireless communication device and waiting for a random timefrom the transmission end, transmission by the plurality of wirelesscommunication devices that grasp the transmission by the wirelesscommunication device stochastically disperses. Therefore, if the numberof wireless communication devices in which the earliest time in a randomtime is subtracted is one, frame transmission by the wirelesscommunication device succeeds and it is possible to prevent framecollision. Since the acquisition of the transmission right based on therandom value becomes impartial between the plurality of wirelesscommunication devices, it can say that a scheme adopting CarrierAvoidance is a suitable scheme to share a radio medium between theplurality of wireless communication devices.

[4] Frame Interval of Wireless LAN

The frame interval of IEEE802.11 wireless LAN is described. There areseveral types of frame intervals used in IEEE802.11 wireless LAN, suchas distributed coordination function interframe space (DIFS),arbitration interframe space (AIFS), point coordination functioninterframe space (PIFS), short interframe space (SIFS), extendedinterframe space (EIFS) and reduced interframe space (RIFS).

The definition of the frame interval is defined as a continuous periodthat should confirm and open the carrier sensing idle beforetransmission in IEEE802.11 wireless LAN, and a strict period from aprevious frame is not discussed. Therefore, the definition is followedin the explanation of IEEE802.11 wireless LAN system. In IEEE802.11wireless LAN, a waiting time at the time of random access based onCSMA/CA is assumed to be the sum of a fixed time and a random time, andit can say that such a definition is made to clarify the fixed time.

DIFS and AIFS are frame intervals used when trying the frame exchangestart in a contention period that competes with other wirelesscommunication devices on the basis of CSMA/CA. DIFS is used in a casewhere priority according to the traffic type is not distinguished, AIFSis used in a case where priority by traffic identifier (TID) isprovided.

Since operation is similar between DIFS and AIFS, an explanation belowwill mainly use AIFS. In IEEE802.11 wireless LAN, access controlincluding the start of frame exchange in the MAC layer is performed. Inaddition, in a case where QoS (Quality of Service) is supported whendata is transferred from a higher layer, the traffic type is notifiedtogether with the data, and the data is classified for the priority atthe time of access on the basis of the traffic type. The class at thetime of this access is referred to as “access category (AC)”. Therefore,the value of AIFS is provided every access category.

PIFS denotes a frame interval to enable access which is morepreferential than other competing wireless communication devices, andthe period is shorter than the values of DIFS and AIFS. SIFS denotes aframe interval which can be used in a case where frame exchangecontinues in a burst manner at the time of transmission of a controlframe of a response system or after the access right is acquired once.EIFS denotes a frame interval caused when frame reception fails (whenthe received frame is determined to be error).

RIFS denotes a frame interval which can be used in a case where aplurality of frames are consecutively transmitted to the same wirelesscommunication device in a burst manner after the access right isacquired once, and a response frame from a wireless communication deviceof the transmission partner is not requested while RIFS is used.

Here, FIG. 28 illustrates one example of frame exchange in a competitiveperiod based on the random access in IEEE802.11 wireless LAN.

When a transmission request of a data frame (W_DATA1) is generated in acertain wireless communication device, a case is assumed where it isrecognized that a medium is busy (busy medium) as a result of carriersensing. In this case, AIFS of a fixed time is set from the time pointat which the carrier sensing becomes idle, and, when a random time(random backoff) is set afterward, data frame W_DATA1 is transmitted tothe communicating partner.

The random time is acquired by multiplying a slot time by a pseudorandominteger led from uniform distribution between contention windows (CW)given by integers from 0. Here, what multiplies CW by the slot time isreferred to as “CW time width”. The initial value of CW is given by CWmin, and the value of CW is increased up to CW max every retransmission.Similarly to AIFS, both CW min and CW max have values every accesscategory. In a wireless communication device of transmission destinationof W_DATA1, when reception of the data frame succeeds, a response frame(W_ACK1) is transmitted after SIFS from the reception end time point. Ifit is within a transmission burst time limit when W_ACK1 is received,the wireless communication device that transmits W_DATA1 can transmitthe next frame (for example, W_DATA2) after SIFS.

Although AIFS, DIFS, PIFS and EIFS are functions between SIFS and theslot-time, SIFS and the slot time are defined every physical layer.Moreover, although parameters whose values being set according to eachaccess category, such as AIFS, CW min and CW max, can be setindependently by a communication group (which is a basic service set(BSS) in IEEE802.11 wireless LAN), the default values are defined.

For example, in the definition of 802.11ac, with an assumption that SIFSis 16 μs and the slot time is 9 μs, and thereby PIFS is 25 μs, DIFS is34 μs, the default value of the frame interval of an access category ofBACKGROUND (AC_BK) in AIFS is 79 μs, the default value of the frameinterval of BEST EFFORT (AC_BE) is 43 μs, the default value of the frameinterval between VIDEO (AC_VI) and VOICE (AC_VO) is 34 μs, and thedefault values of CW min and CW max are 31 and 1023 in AC_BK and AC_BE,15 and 31 in AC_VI and 7 and 15 in AC_VO. Here, EIFS denotes the sum ofSIFS, DIFS, and the time length of a response frame transmitted at thelowest mandatory physical rate. In the wireless communication devicewhich can effectively takes EIFS, it may estimate an occupation timelength of a PHY packet conveying a response frame directed to a PHYpacket due to which the EIFS is caused and calculates a sum of SIFS,DIFS and the estimated time to take the EIFS.

Note that the frames described in the embodiments may indicate not onlythings called frames in, for example, IEEE 802.11 standard, but alsothings called packets, such as Null Data Packets.

When it is expressed that the plurality of terminals transmits/receivesa plurality of frames or a plurality of X-th frames, the frames or theX-th frames may be the same (for example, the same type or the samecontent) or may be different. An arbitrary value can be put into Xaccording to the situation.

The terms used in each embodiment should be interpreted broadly. Forexample, the term “processor” may encompass a general purpose processor,a central processing unit (CPU), a microprocessor, a digital signalprocessor (DSP), a controller, a microcontroller, a state machine, andso on. According to circumstances, a “processor” may refer to anapplication specific integrated circuit (ASIC), a field programmablegate array (FPGA), and a programmable logic device (PLD), etc. The term“processor” may refer to a combination of processing devices such as aplurality of microprocessors, a combination of a DSP and amicroprocessor, or one or more microprocessors in conjunction with a DSPcore.

As another example, the term “memory” may encompass any electroniccomponent which can store electronic information. The “memory” may referto various types of media such as a random access memory (RAM), aread-only memory (ROM), a programmable read-only memory (PROM), anerasable programmable read only memory (EPROM), an electrically erasablePROM (EEPROM), a non-volatile random access memory (NVRAM), a flashmemory, and a magnetic or optical data storage, which are readable by aprocessor. It can be said that the memory electronically communicateswith a processor if the processor read and/or write information for thememory. The memory may be arranged within a processor and also in thiscase, it can be said that the memory electronically communication withthe processor. The term “circuitry” may refer to not only electriccircuits or a system of circuits used in a device but also a singleelectric circuit or a part of the single electric circuit. Moreover, theterm “circuitry” may refer one or more electric circuits disposed on asingle chip, or may refer one or more electric circuits disposed on aplurality of chips more than one chip or a plurality of devices in adispersed manner.

In the specification, the expression “at least one of a, b or c” is anexpression to encompass not only “a”, “b”, “c”, “a and b”, “a and c”, “band c”, “a, b and c” or any combination thereof but also a combinationof at least a plurality of same elements such as “a and a”, “a, b and b”or “a, a, b, b, c and c”. Also, the expression is an expression to allowa set including an element other than “a”, “b” and “c” such as “a, b, c,and d”.

While certain embodiments have been described, these embodiments havebeen presented by way of example only, and are not intended to limit thescope of the inventions. Indeed, the novel embodiments described hereinmay be embodied in a variety of other forms; furthermore, variousomissions, substitutions and changes in the form of the embodimentsdescribed herein may be made without departing from the spirit of theinventions. The accompanying claims and their equivalents are intendedto cover such forms or modifications as would fall within the scope andspirit of the inventions.

Additional advantages and modifications will readily occur to thoseskilled in the art. Therefore, the invention in its broader aspects isnot limited to the specific details and representative embodiments shownand described herein. Accordingly, various modifications may be madewithout departing from the spirit or scope of the general inventiveconcept as defined by the appended claims and their equivalents.

The invention claimed is:
 1. A wireless communication device comprising:a receiver configured to receive a first type of frame for UL-OFDMA(Uplink Orthogonal Frequency Division Multiple Access) random accessincluding first information that specifies a plurality of frequencycomponents; controlling circuitry configured to determine whether torespond to the first type of frame, based on a first value selectedrandomly from a first value range and a number of the plurality offrequency components; and a transmitter configured to, in response todetermining to respond to the first type of frame, select one frequencycomponent from the plurality of frequency components and transmit asecond type of frame for response to the first type of frame using theselected frequency component, wherein the controlling circuitry isconfigured to determine whether transmission of the second type of framehas succeeded or failed, and adjust the first value range based on aresult of determining whether transmission of the second type of framehas succeeded or failed, the first information includes informationrelating to the number of the plurality of frequency components, thecontrolling circuitry is configured to specify the plurality offrequency components based on the first information, the first type offrame includes second information designating a certain terminal totransmit the second type of frame using a second frequency componentdifferent from the plurality of frequency components for the UL-OFDMArandom access, the controlling circuitry is configured to determinewhether the wireless communication device is designated in the secondinformation as the certain terminal, in response to a determination thatthe wireless communication device is not designated in the secondinformation as the certain terminal, determine whether to respond to thefirst type of frame based on the first value and the number of theplurality of frequency components, and in response to a determinationthat the wireless communication device is designated in the secondinformation as the certain terminal, not determine whether to respond tothe first type of frame based on the first value and the number of theplurality of frequency components, and the transmitter is configured toin response to a determination that the wireless communication device isdesignated in the second information as the certain terminal, transmitthe second type of frame using the second frequency component.
 2. Thewireless communication device according to claim 1, wherein thecontrolling circuitry is configured to determine whether to respond tothe first type of frame based on the first value and the number of theplurality of frequency components only when the wireless communicationdevice has a request for uplink transmission.
 3. The wirelesscommunication device according to claim 1, wherein, the controllingcircuitry is configured to select the first value from the first valuerange only when the wireless communication device has a request foruplink transmission.
 4. The wireless communication device according toclaim 1, wherein, the first value range is a contention window forUL-OFDMA and the first value is a back off count value randomly selectedfrom the contention window for UL-OFDMA.
 5. A wireless communicationmethod comprising: receiving a first type of frame for UL-OFDMA (UplinkOrthogonal Frequency Division Multiple Access) random access includingfirst information to specify a plurality of frequency components whereinthe first information includes information that specifies a number ofthe plurality of frequency components; determining whether to respond tothe first type of frame, based on a first value selected randomly from afirst value range and the number of the plurality of frequencycomponents; specifying the frequency components based on the informationincluded in the first information, and in response to determining torespond to the first type of frame, selecting one frequency componentfrom the plurality of frequency components; transmitting a second typeof frame for response to the first type of frame for using the selectedfrequency component; determining whether transmission of the second typeof frame has succeeded or failed; and adjusting the first value rangebased on a result of determining whether transmission of the second typeof frame has succeeded or failed, wherein the first type of frameincludes second information designating a certain terminal to transmitthe second type of frame using a second frequency component differentfrom the plurality of frequency components for the UL-OFDMA randomaccess, the method comprises determining whether the wirelesscommunication device is designated in the second information as thecertain terminal, in response to a determination that the wirelesscommunication device is not designated in the second information as thecertain terminal, determining whether to respond to the first type offrame based on the first value and the number of the plurality offrequency components, in response to a determination that the wirelesscommunication device is designated in the second information as thecertain terminal, not determining whether to respond to the first typeof frame based on the first value and the number of the plurality offrequency components, and in response to a determination that thewireless communication device is designated in the second information asthe certain terminal, transmitting the second type of frame using thesecond frequency component.
 6. The wireless communication deviceaccording to claim 1, wherein the first type of frame has an AID(Association ID) field, and the second information is included in theAID field.
 7. The wireless communication device according to claim 1,wherein the first type of frame has an AID field, and a second valueindicating that the plurality of frequency components can be used forthe UL-OFDMA (Uplink Orthogonal Frequency Division Multiple Access)random access is included in the AID field.
 8. The wirelesscommunication device according to claim 7, wherein the second value is avalue defined beforehand by a standard.
 9. The wireless communicationdevice according to claim 7, wherein the second value is a value of anAID not assigned to any terminal.
 10. The wireless communication deviceaccording to claim 7, wherein the first type of frame includes at leastone terminal information field, the terminal information field includesthe AID field and a first field, and one of the plurality of frequencycomponents is included in the first field.
 11. The wirelesscommunication device according to claim 7, wherein the terminalinformation field further includes a second field, and information tospecify at least one of a MCS (Modulation and Coding Scheme) or atransmission power for the UL-OFDMA is included in the second field. 12.The wireless communication device according to claim 1, furthercomprising at least one antenna.
 13. The wireless communication deviceaccording to claim 1, further comprising a memory.
 14. The wirelesscommunication device according to claim 1, further comprising a CPU(Central Processing Unit).
 15. The wireless communication deviceaccording to claim 1, further comprising a display.